Agricultural Ecosystems Program: Understanding Sources and Sinks of Nutrients
and Sediment in the Upper Susquehanna River Basin
Project Description.
Objectives:
Our goal is to gain a better understanding of the sources and sinks of nitrogen (N),
phosphorus (P), and sediment in a large rural watershed of mixed land use, including
agricultural and forest lands. The geographic focus is the Susquehanna River drainage
basin and its tributaries within New York State (an area of approximately 19,500 km2),
with an emphasis on N and P dynamics of the agricultural and forested landscapes of the
region. The Susquehanna is the largest river east of the Mississippi in the US, the largest
tributary of Chesapeake Bay, and the single largest source of nutrients to the main stem
of the Bay. Thus, better understanding the sources and sinks of nutrients and sediment in
the Susquehanna can lead towards better management of nutrient fluxes from the
landscape and thus water quality in Chesapeake Bay. The proposed research will also
lead to a better understanding of the controls on nutrient pollution – particularly N
pollution – in rural landscapes in general, and to insights on sustaining agriculture in the
northeastern US in a manner that best harmonizes with environmental quality. A major
sub theme will be how climate variability and climate change influence the fluxes of N,
P, and sediments from the rural landscape. N is the primary focus, both because it is the
primary pollution problem in coastal systems such as Chesapeake Bay, and because
sources and sinks are more poorly understood than for P. Nonetheless, much can be
gained from simultaneous study of the dynamics of N, P, and sediments.
Progress Report: This will be a new project.
Justification and Literature Review:
The human acceleration of the N cycle is one of the most pronounced aspects of global
change, with the rate of increase in the formation of reactive N far exceeding the rate of
accumulation of CO2 in the atmosphere (Vitousek et al. 1997). The increased supply of
N is a serious threat to the ecological functioning of a variety of ecosystems, including
forests, streams, and lakes in addition to coastal marine ecosystems (Vitousek et al.
1997). However, coastal marine ecosystems are particularly at risk from N pollution, and
N is now the largest pollution problem in the coastal waters of the U.S. (Nixon 1995;
NRC 2000; Howarth et al. 2000; Rabalais 2002). N pollution also poses significant
risks to human health in a variety of ways, including contamination of groundwater and
drinking water and reduction in rural and urban air quality (Townsend et al. 2003).
N pollution in coastal systems has grown over the past few decades (NRC 2000;
Howarth et al. 2000). The resulting eutrophication lowers biotic diversity, leads to
hypoxic and anoxic conditions, increases the incidence and duration of harmful algal
blooms, degrades the habitat quality of seagrass beds or even completely destroys them,
and can lead to changes in ecological food webs that lower fishery production (NRC
2000). The National Coastal Condition Report (EPA 2001) lists eutrophic condition as
one of the three greatest threats to the health of the nation’s estuaries, along with poor
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benthic condition (itself due to eutrophication, in part) and wetland loss. Some 40% of
the estuarine area in the conterminous U.S. is severely degraded from eutrophication, and
67% is degraded to some extent (Bricker et al. 1999; EPA 2001). In the northeastern
US, some 60% of estuarine area shows a high expression of eutrophic condition (EPA
2001). Both a “white-paper panel” of the Ecological Society of America (Vitousek et al.
1997) and the Coastal Marine Team of the National Climate Change Assessment (Boesch
et al. 2000; Scavia et al. 2002) concluded that N pollution is one of the greatest
consequences of human accelerated global change on the coastal oceans of the world.
The societal implications are immense, as estuaries are among the most valuable of all
ecosystems with regard to the services they provide (Costanza et al. 1997).
Only recently has a national consensus of water quality managers evolved that N rather
than P is the prime cause of eutrophication in coastal marine ecosystems (NRC 2000;
Howarth and Marino, in press). In sharp contrast, P is the leading cause of eutrophication
in lakes, and P control has been the prime focus of water quality management in the U.S.
for most of the past 3 decades. This focus on P led to much more research on sources and
sinks of P in the landscape, and means to reduce inputs to surface waters. The knowledge
base on sources of N is more limited, and more recent. Compared to P, N is much more
mobile in the environment, with significant fluxes both through groundwater and
atmospheric pathways. N also has significant biological sources and sinks through the
microbial processes of N fixation and denitrification, adding to the complexity of the N
cycle. This complexity poses significant challenges for understanding the sources of N
pollution (NRC 2000; Howarth et al. 2002b). However, P can also contribute to
degradation of water quality in coastal systems, and there is great value in studying the
cycles of N and P in consort (NRC 2000; Howarth and Marino, in press).
The distribution of reactive N is far from uniform across the planet, and N pollution in
coastal waters is greatest where agricultural activity and urbanization and air pollution are
greatest. In some regions such as the North Sea and Yellow Sea, human activity
probably has increased N fluxes to the coast by 10- to 15-fold or more, while in other
areas such as Hudson’s Bay and Labrador, human activity probably has had little effect
on N fluxes (Howarth 2003). On average for the US, human activity has increased N
fluxes to the coast by an estimated 6-fold (Howarth et al. 2002a; Howarth 2003).
Currently, the greatest increase in N pollution is occurring in Asia, particularly in China
(Galloway et al. 2004). The increase in N inputs to coastal waters in the US was
particularly dramatic in the 1960s and 1970s; since then, the rate of increase has slowed,
yet N inputs to coastal waters in the US have continued to increase on average by ~1%
per year over the past 15 years (Howarth et al. 2002a).
The single largest driver globally in acceleration of N cycling is the increased use of
synthetic N fertilizer in agriculture, and half of the synthetic fertilizer that has ever been
used on Earth has been applied in the past 15 years or so (Howarth et al. 2002b;
Galloway et al. 2004). The combustion of fossil fuel also inadvertently creates reactive
N. While globally the creation of reactive N from burning fossil fuels amounts to only
25% of the rate of N fertilizer synthesis (Galloway et al. 2004), in the US the atmospheric
emissions and deposition of N from fossil fuel are relatively more important, at ~ 60% of
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the rate of use of synthetic N fertilizer (Howarth et al. 2002a). In many watersheds in the
northeastern US, atmospheric deposition of N that originates from fossil fuel sources is a
greater source of N than is fertilizer use (Boyer et al. 2002). Often, there is considerable
uncertainty in the relative magnitudes of N sources in particular watersheds (NRC 2000).
For example, for the watersheds of Chesapeake Bay including the Susquehanna, studies
differ as to whether agricultural sources or atmospheric deposition onto the landscape are
more important contributors of N (Magnien et al. 1995; Jaworski et al. 1997; NRC
2000; Boyer et al. 2002; Howarth et al. 2002b). Recent evidence suggests that the
actual magnitude of atmospheric deposition onto the watersheds of Chesapeake Bay may
have been underestimated severely in the past due to lack of consideration of high
deposition near emission sources (Howarth et al., in press).
The uncertainty over the importance of atmospheric N deposition as a source of N
pollution to surface waters stems from two issues: 1) the extent of dry deposition of N
onto the landscape; and 2) the fate of the N that is deposited onto the landscape. The
vast majority of measurements of N deposition – including those of the National
Atmospheric Deposition Program (NADP) -- measure only wet deposition (N in rainfall
and snow) or bulk deposition (wet deposition plus N deposited in open buckets during
dry weather periods). Measurements of bulk deposition can substantially underestimate
dry deposition and hence total N deposition, the sum of wet plus dry deposition (Lovett et
al. 2000). Often, dry deposition (which includes aerosols and other particles and uptake
of gaseous forms of N by vegetation, soils, and surface waters) is assumed to roughly
equal rates of wet N deposition, but this assumption has a very limited data base to
support it (Holland et al. 1999; Howarth et al. 2002b). Dry deposition is routinely
measured in the US only at the limited number of sites that are part of the CASTNet and
AIRMon-Dry programs. For N, not all of the components of gaseous dry deposition are
measured (for example, NH3 and NO2 are not measured). Further, all of the CASTNet
and AIRMon-Dry sites are deliberately chosen to estimate background levels of
deposition and as such are located well away from emission sources. However, recent
evidence suggests that dry deposition, particularly of gaseous N species, may often be
substantially higher near emission sources, both for oxidized N gases and for ammonia
(Fahey et al. 1999; Lovett et al. 2000; Cape et al. 2004; Howarth et al., in press).
Also highly uncertain is the fate of N that is deposited onto the landscape. Many models
assume that N is tightly retained in forests (Magnien et al. 1995). However, recent
syntheses of the effects of N deposition on temperate forests indicate that stream nitrate
export often increases sharply as deposition increases above a threshold of approximately
8 to 10 kg N ha-1 y-1 (NRC 2000; Howarth et al. 2002b; Aber et al. 2003). This
threshold effect is critical for understanding the fate of N in the upper Susquehanna River
Basin, since this area receives some of the highest rates of N deposition in the country.
Total (wet + dry) inorganic N deposition in the Upper Susquehanna Basin exceeds 10 kg
N ha-1 y-1, or more than ten times pre-industrial background conditions (Holland et al.
1999). However, variability in stream N export increases with N loading as well: that is,
some, but not all watersheds increase N export with elevated N inputs. Variability among
watersheds receiving similar rates of N deposition can be quite large, with stream
inorganic N exports ranging from 2% to 50% of inputs (Aber et al. 2003). Factors
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driving variation among watersheds may include differences in tree species composition
(Lovett et al. 2000), past land-use history and stand age (Goodale et al. 2000), and
variation in hydrologic flowpaths across watersheds or through time (Creed & Band
1998; Burns & Kendall 2002). Retention of N in soils and vegetation is expected to be
greatest in old-field sites reverting to forest, with rates of N accumulation decreasing as
stands age (Aber et al. 1998, 2003).
The contribution of N and P to surface waters from agricultural sources is highly
dependent on a variety of management practices, including cropping systems and amount
and timing of fertilizer application, as well as on soil type and climate (NRC 1993;
Randall et al. 1997; Randall and Mulla 2001; Sogbedji et al. 2000, 2001; van Es et al.
2002; Howarth et al. 2002b; Kahabka et al., 2004). On average for the US, about 20%
of the fertilizer N inputs to agricultural fields leach to surface or ground waters (NRC
1993; Howarth et al. 2002a). The variability among fields is great, though, ranging from
a low for leaching loss of 3% for grasslands with clay-loam soils to 80% for some rowcrop agricultural fields on sandy soils (Howarth et al. 1996). These results provide the
opportunity to directly investigate management strategies to reduce off-site effects. The
choice of cropping system is particularly important for influencing nutrient loss; for
example, fields planted to perennial alfalfa lost 30- to 50-fold less nitrate than did fields
planted in corn and soybeans in Minnesota and Iowa (Randall et al. 1997; Randall and
Mulla 2001). Planting of winter cover crops can also be important for reducing nutrient
losses; an experimental study in Maryland showed the long term effect of winter covercrop plantings was a 3-fold reduction in nitrate loss (Staver and Brinsfield 1998).
Interestingly, while no-till agriculture significantly reduces sediment and P losses from
fields by reducing erosion, it has little if any effect on N losses (Randall and Mulla 2001).
In fact, reduced tillage may also increase N leaching through the preservation of pore
continuity that enhances drainage (Andreini and Steenhuis, 1990). Organic N from
manure and converted sods is often introduced at a time (i.e., autumn) when little plant
uptake occurs and as such the leaching losses are high (Sogbedji et al. 2000, 2001; van Es
et al. 2002). Also, farmers typically ignore the seasonal variations in crop N needs due to
weather conditions. Randall and Mulla (2001) demonstrated in Minnesota that fall
application of fertilizer resulted in 305 to 40% greater N losses from fields over the year
compared with spring or summer application. Similarly, fall application of manure
results in high nitrate leaching losses on many dairy farms in New York (van Es et al.,
2002) and also results in higher N fertilizer rates ( Howarth et al. 2002a).
Annual weather variability additionally contributes to inefficient N use on farms.
Seasonal N needs are strongly influenced by weather conditions in that optimum fertilizer
rates are higher in years with wet springs due to rapid leaching and dentrification
(Sogbedji et al., 2001). Conversely, optimum N rates are considerable lower in dry years,
but farmers still fertilize for the highest N demand, contributing to excessive
(“insurance”) applications. This is especially critical because high residual N in dryer
years poses the greatest concern for water contamination (McIsaac et al., 2001). It is
believed that substantial reduction in environmental N losses may be achieved through
more precise N management on farms.
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The intensification of animal production systems, with major importation of feeds into a
region, also contributes greatly to surface water pollution of P and N (NRC 2000;
Howarth et al. 2002a, 2002b). A study of four northeast dairy farms by Klausner et al.
(1998) showed approximately two-thirds of the N and phosphorous imported onto the
farms was retained on a dairy farm or was unaccounted for while only a third was
exported as milk, meat or crops. Many of the farm imports of N and P are animal feeds
which are subsequently excreted as manure and land applied in excess of crop
requirements. This can lead to direct nutrient losses to surface and groundwater as well as
indirect losses when nutrients such as P accumulate and cause increasingly high fertility
levels. Nitrate tests from wells on corn fields at Cornell’s Teaching and Research Center
in Harford, NY, a dairy farm with 360 cows, increased from 3.3 to 7.0 mg kg-1 over a 15year period when feed imports increased 40%. During the same period on the same fields,
soil P levels increased 4-fold to 24 kg ha-1 (Wang et al. 1999). In New York State,
currently 47% of the soils test above the agronomic optimum for P compared to 26% in
the early 1980s (Ketterings et al., 2005). Further, ammonia volatilization from animal
wastes can distribute N across the landscape, and may be a major contributor to N
pollution in surface waters (NRC 2000; Howarth et al. 2002b). Fahey et al. (1999)
demonstrated that across Tompkins County, NY (the home of Cornell University, and a
landscape that is very close to and very similar to most of the upper Susquehanna River
Basin) atmospheric deposition of ammonia/ammonium varied greatly in space, and was
presumably much higher near agricultural sources.
Climate variability and climate change are likely to have a profound effect on the
movement from the landscape and delivery of nutrients in rivers to coastal marine
ecosystems, but there is great uncertainty as to the detailed responses expected (Boesch et
al. 2000; Scavia et al. 2002). This uncertainty results in part from divergent predictions
for future climate change, for example with some global models predicting a drier climate
and some a wetter climate in the northeastern US as atmospheric carbon dioxide levels
continue to rise over the next century (Wolock and McCabe 1999). Further uncertainty
results from the non linearity in response of riverine freshwater discharge to changes in
climate, with some models suggesting discharge will increase disproportionately to
increases in precipitation, and others suggesting increases in discharge will be less than
increases in precipitation (Najjar 1999; Wolock and McCabe 1999; Najjar et al. 2000).
Beyond these uncertainties in the physical climate system and the hydrologic responses
of watersheds, the biogeochemical responses to changes in climate and hydrology are
difficult to predict, particularly for N.
Watersheds with greater precipitation and discharge will tend to have higher erosion
rates, and this leads to higher fluxes of sediment and P from the landscape since most of
the P in large rivers is particle bound (Moore et al. 1997; Howarth et al. 1995, 2002b).
N moves through the landscape primarily in dissolved forms, and N fluxes seem to be
primarily controlled by the balance of sources and sinks of N in the landscape. For
disturbed landscapes in the temperate zone, an average of 20 to 25% of the N inputs
resulting from human activity is exported in rivers (Howarth et al. 1996, 2002b; Boyer et
al. 2002). However, there is a pronounced climatic overlay on this. For the Mississippi
River basin, McIsaac et al. (2001) demonstrated that during dry years, N accumulates in
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the soil or groundwater, and during wet years, this stored N is flushed out. There also is a
steady-state influence of climate on N fluxes in rivers. In a comparative analysis of 16
large watersheds, Howarth et al. (in press) showed that the long-term, average fraction of
human N inputs exported from the landscape downstream varied from as little as 10% in
watersheds with relatively low precipitation and freshwater discharge to 40% or greater
in watersheds with higher precipitation and higher discharge. Presumably, this reflects a
greater loss of N from denitrification in the watersheds with lower precipitation and
discharge. While this may seem paradoxical since denitrification is favored by
waterlogged soils, the over-riding control may be water residence time (Seitzinger et al.
2002). In the watersheds with more precipitation and greater discharge, water may flow
through zones of potentially high activity, such as riparian wetlands and first-order
streams too quickly for significant denitrification to occur (Howarth et al., in press).
Conversely, N use is contributing significantly to climate change. Nitrous oxide (N2O) is
a greenhouse gas and is also detrimental to the ozone layer (Vitousek et al. 1997).
Although the gas is emitted in much lower quantities than CO2, it is 310-fold more
effective as a greenhouse gas (per mass), and N2O is responsible for 7.5 per cent of the
calculated greenhouse effect caused by human activity (IPCC 2001). The concentration in
the atmosphere is increasing at a rate of about 0.2 per cent per year. Agricultural soils are
thought to be the major source of atmospheric N2O at the global scale globally. All forms
of N fertilizer can lead to N2O emissions, and timing and rates of application are
important modulating factors (Tan et al. 2005), and need to be considered concomitantly
with water quality concerns.
Our proposed research program is designed to gain a better understanding of the sources
of N and P flux within and from the upper Susquehanna River basin, an area that typifies
much of the rural northeastern US and is also a direct contributor of N, P, and sediment to
Chesapeake Bay. A federal interagency research plan for nutrient pollution developed in
2003 by NOAA, USDA, EPA, and NSF identifies the sort of research we propose here on
better source characterization as one of the top national research priorities (Howarth et al.
2003). The proposed research should lead towards a better understanding of direct
relevance to sustaining agriculture in the northeastern US in a manner that best
harmonizes with environmental quality. We will specifically evaluate the importance of
agricultural sources of nutrient pollution in the context of all sources in the watershed.
The Cornell community has broad expertise in the disciplines required to achieve the
goals. The proposed program is designed to foster creative new research and integrate
the results with current research at Cornell into an overall, comprehensive effort that can
have an impact larger than the sum of its parts.
The Upper Susquehanna River Basin study region:
The proposed work will focus on understanding the sources and sinks of N, P, and
sediment in the drainage basin of the Susquehanna River and its tributaries within New
York State (an area of ~ 19,500 km2), with an emphasis on N. The Susquehanna is the
largest river east of the Mississippi in the US, the largest tributary to Chesapeake Bay,
and the single largest source of nutrients to the main stem of the Bay (Hagy et al. 2004;
Chesapeake Executive Council 2004). Chesapeake Bay, in turn, is the largest estuary in
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the US, and one of the most sensitive to the adverse effects of N pollution (NRC 2000).
Approximately 25% of the entire Susquehanna River basin is in New York State.
Over the past few decades, N inputs to Chesapeake Bay have severely degraded water
quality, with increasing volumes of oxygen-free waters devoid of fish life and the dieback
of critical seagrass-bed habitat. In the 1980s, Maryland, Virginia, and Pennsylvania
together with the US EPA agreed to reduce the inputs of N from controllable sources to
the Chesapeake by 40% (Chesapeake Executive Council 1983, 1987). Despite significant
efforts in these states, however, N inputs remain high, and water quality has improved
little if at all (NRC 2000). As a result, the Chesapeake Bay Program (run by the US
EPA), the Chesapeake Bay Commission, and the 6 states in the watershed of Chesapeake
Bay have committed to further, stringent reductions in N, P, and sediment to the Bay
(Chesapeake Executive Council 2000, 2004). Governor Pataki formally committed New
York State to this goal in March of 2004. The proposed cap for N fluxes from New York
State down the Susquehanna (to be reached by 2010) is 5,700 metric tons per year, which
is a 26% reduction according to the estimates of the Chesapeake Bay model (Chesapeake
Executive Council 2004). However, there is significant uncertainty in the current flux, as
models differ in their estimation of the magnitude and routine monitoring has only begun
in the past year. Also, climate variability and future climate change may tend to increase
N fluxes in the Susquehanna, making it more difficult to reach the targeted reductions
(Howarth et al., in press). Failure to meet this goal is likely to result in mandatory N and
P reductions imposed by the EPA (Chesapeake Executive Council 2004).
The national importance of Chesapeake Bay, and the importance to the continued
viability of New York State agriculture to meet the 2010 nutrient caps, provide strong
justifications for the research we propose. More broadly, we view the upper
Susquehanna River basin as an ideal “laboratory” for better understanding the factors that
control N fluxes from rural landscapes with mixed agriculture and forest lands. The land
use in the Susquehanna River basin is overwhelmingly rural, and the landscape is an
interacting mixture of farmland (29% of the area) and forests (67% of the area; Boyer et
al. 2002). The majority of this forest land was once in agriculture, and approximately 5%
is in recently abandoned farmland reverting to forest (Laba et al. 2002). The rate of
atmospheric deposition of oxidized N (NOy, which in this region originates largely from
fossil fuel combustion) onto this landscape is amongst the highest in any rural area in the
US (Holland et al. 1999; Boyer et al. 2002). Due to soil and landscape factors, most
intensive agricultural activities in the Upper Susquehanna Basin are located near streams,
and a large fraction is animal-based (mostly dairy). Moreover, the lands receiving N as
manure and fertilizer are often coarse-textured valley-bottom soils that have high
leaching potentials. This has created a situation where N may be readily discharged into
the stream system through shallow groundwater. Most of the upper Susquehanna River
basin is within a 10 minute to 1.5 hour drive of Cornell University, making it a
convenient area of study for our faculty, staff, and students.
In 2004, the North American N Center was established at Cornell University as part of
the International N Initiative (a joint effort of the International Council of Science’s
IGBP and SCOPE programs). The goals of the Center are to better understand the
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sources and sinks of N across North America, to quantify the consequences of N
pollution, and to provide scientific support for the development of technical and policy
approaches for reducing N pollution (www.eeb.cornell.edu/biogeo/nanc/nanc.htm). The
N Center has identified an improved understanding of N sources and sinks in
Susquehanna River Basin as a priority area of study in North America, for the reasons
presented above. This proposed research will directly support this priority.
Procedures and Approach to Research:
Our proposed research falls into two categories: 1) integrated modeling of nutrient and
sediment sources and sinks across spatial scales; and 2) a series of creative, spin-up
efforts emphasizing field or laboratory studies leading toward a better understanding of
the sources and sinks of nutrients and sediments in the Susquehanna River Basin. For
both of these, much of the research will be focused around two core sites within the basin
that have long-term data records, one an agricultural site and one an atmospheric
deposition site. These approaches to research and the research sites are described in
detail below. The research addresses the dual needs for better understanding of the
biophysical processes affecting N losses in the Basin, as well as the identification of
management options for watershed abatement efforts. Although the processes controlling
P fluxes are better understood, and P is less of a problem in Chesapeake Bay and most
other coastal systems, much can be gained from studying N and P together (NRC 2000;
Howarth & Marino, in press), and that is the approach we propose. These approaches to
research and the research sites are described in detail below.
Integrated modeling across scales:
We will use 2 models at the scale of the entire upper Susquehanna River basin: the
SCOPE/NANI model and the Regional Nutrient Management model (ReNuMa). We will
explore how the insights and output from several smaller scale models can interact with
these large watershed-scale models. The SCOPE/NANI model is a simple mass-balance
model for N that compares sources of N in the landscape to riverine N fluxes. It was
originally developed for large regions, such as the combined watersheds of the North Sea
or the northeastern US, or the entire Mississippi River basin (Howarth et al. 1996), but
has subsequently been applied to watersheds of the scale of the Susquehanna both in the
U.S (Boyer et al. 2002) and in Europe (Humborg and colleagues, unpublished). Despite
its simplicity, a comparative analysis of many models demonstrated that the
SCOPE/NANI model is among the best in terms of error of prediction and assessment of
N source determination (Alexander et al. 2002). The model when employed as we and
most others have previously used it evaluates average N fluxes over periods of 6 to 10
years, but McIsaac et al. (2001) used a modification of the approach to accurately predict
year-to-year variations in N flows in the Mississippi River that are associated with
climatic variation. We will test this approach for the Susquehanna, in an effort to better
determine the influence of climate on overall N fluxes, and to get insights into the relative
importance of climate effect on different N source terms (Howarth et al., in press.).
The other model we will use at the large watershed scale is ReNuMa, a model designed
to allow planners and other stakeholders to explore scenarios for reducing N fluxes
from the landscape. We have been funded by the US EPA to develop ReNuMa, which
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is a refinement of the GWLF model of Haith and Shoemaker (1987). This lumped
parameter model is an excellent predictor of freshwater discharge for the Hudson River
and its tributaries on a fine temporal scale, and a good predictor of inputs of sediment
and organic carbon on a monthly to seasonal time scale (Howarth et al. 1991; Swaney
et al. 1996). GWLF has also been used to estimate nutrient loads into the Delaware
River (Haith and Shoemaker 1987), the Tar-Pamlico estuary (Dodd and Tippett 1994),
and the Choptank River drainage of Chesapeake Bay (Lee et al. 2000, 2001).
However, the characterization of the N cycle within GWLF is excessively simple. For
example, it does not include denitrification, which is the major sink for N in most
watersheds (van Breemen et al. 2002). Rather, nutrients are transported passively, and
within-soil, riparian-zone, and in-stream processes are not considered. GWLF also
does not explicitly consider atmospheric inputs of N, even though these are the major
nonpoint sources of N to many waters and watersheds in the northeastern US and
elsewhere (Howarth et al. 1996, 2002b; NRC 2000; Boyer et al. 2002). Further,
GWLF assumes specified values for nutrient concentrations from fertilizer or manure
applications, irrespective of management practices and other mitigating factors. In
developing ReNuMa, we are adding modules to better capture biogeochemical
complexity and the relationship between hydrology and nutrient sources and sinks in
the landscape, as well as for the effects of management practices on nutrient loads. We
have limited funding from the USDA Hatch program ($15,000 per year) to begin to
apply ReNuMa to the Susquehanna basin. This additional funding will enhance our
ability to parameterize the model to the Susquehanna. We also propose to use output
from the SCOPE/NANI model to improve the ability of ReNuMa to predict the
consequences of climate variability and climate change on delivery of N. And we will
use insights gained from plot- to farm-scale models to better parameterize the
responses of ReNuMa to agricultural practices (see discussion below on these models).
Both the SCOPE/NANI approach and ReNuMa will be ground-truthed against the
accumulating body of data on fluxes of water, N, P, and sediments from the upper
Susquehanna River basin being collected by the USGS, the NYS DEC, and others.
There are a large number of models that address fluxes of nutrients at the scale of plots to
farm fields to whole farms, including several models developed and used by Cornell
faculty and staff. These models often have a great deal more complexity and spatial
reality than do the coarser scale large watershed models such as SCOPE/NANI and
ReNuMa. On the other hand, their complexity and detail tend to make them difficult to
scale up to give reliable estimates on watershed-scale nutrient fluxes (NRC 2000). Using
insights gained from one scale of modeling to inform modeling at a different spatial
scale, although challenging, is highly desirable. We propose to facilitate such an
interaction of modeling efforts across scales in the Susquehanna River basin. One goal is
to improve the utility of the integrative watershed model ReNuMa, as stated above.
Beyond this, we believe the cross-fertilization of ideas may lead to improved models at
smaller scales as well, and to an improved understanding of the processes that are critical
in determining the fluxes and sinks of N and P (and where in the landscape such
processes may be most important to understand). One approach to crossing this scale
divide includes statistical comparisons of model outputs when models are subject to
similar input perturbations, such as extreme weather events. Another approach is to use
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the model research at smaller scales to better identify and describe the critical processes
that may control the overall behavior of large watersheds. For example, preferential
flowpaths may be characterized by their relationship to soil types. Various categories of
land and crop management may be summarized in terms of their effects on hydrology,
soil loss, or chemical processes. This level of information can be considered a
“typology” or classification system derived from detailed process studies, and can in turn
be used as a basis for simplified models or “decision support tools” at larger scales. An
approach like this has been taken in Sweden to develop the SOILNDB system, based on
the models SOIL and SOILN (http://www.mv.slu.se/vv/model/e_soilndb.htm).
Given the large number of smaller scale models of potential value to the overall goals of
the project, we propose to have a competitive process for selecting both for the model
studies that may offer the best opportunity to scale up insights, and for researchers who
are most open to undertaking this challenging endeavor. The expectation is that support
will be available for 2 to 3 modeling efforts, developed over a multi-year time period.
The required emphasis for supported research will be on integration across scales, and
understanding the flows of nutrients and sediment in the Susquehanna, and not on the
development of new models per se. Thus, the expectation is that only small spatial scale
modeling efforts that already have other sources of support will be further funded by this
Susquehanna project. An example of one such model is the recently-developed PNM
(Precision N Management) model that allows for simulation of soil N dynamics and crop
uptake and can be applied to better estimate seasonal crop N needs as well as predict N
leaching from the soil profile. This model can also be used to estimate N losses from
organic and inorganic sources on agricultural fields in the basin and to evaluate potential
reductions in environmental losses from alternative management practices. Another
example model might be a statistical meta-data analysis that relates nitrate concentrations
below rooting zones to agricultural practices across a broad range of soils types and
climate. And a third example model might be the Soil Moisture Routing Model (SMR)
developed at Cornell for small watersheds where soil saturation is largely controlled by
interflow (Zollweg et al. 1996; Frankenberger et al. 1999). This hydrologic model works
with a grid size of 10 m X 10 m and has recently been applied to estimating the loss of P
from manures applied to fields (Gérard-Marchant et al. 2005). Again, these models are
given here just as examples, and we anticipate that other modeling projects will be
proposed by Cornell faculty, staff, and students as part of this competition. We will use
peer-review and a selection committee to choose those deemed most likely to fulfill the
overall Agricultural Ecosystem Program goals. We will also develop processes to ensure
interaction and integration among these modeling projects (such as regular meetings).
Creative spin-up research efforts:
The Cornell community has extensive depth of expertise that can support the central
research objectives, and we propose to tap into this in a manner to maximize the
development of new, creative science. Towards this end, the project will support a series
of meso-size start-up grants for new research efforts directly related to the overall project
objectives and a series of mini-grants to augment current research and encourage its
application to the understanding of the Susquehanna River basin. These awards will be
made on a competitive basis to faculty, staff, and students in the College of Agriculture
10
and Life Sciences and related departments. We envision supporting four of the meso-size
grants, averaging $30,000 each year over two years (contingent on future funding). The
expectation is that some of these will lead to larger, more sustained research in the
Susquehanna Basin, using other sources of support. The research can be at a variety of
spatial scales (micro, plot-scale, farm or small watershed scale, or large watershed), and
can be either lab- or field-based, but it must be directly applicable to understanding
nutrient fluxes in the landscape of the Susquehanna and opportunities to reduce
downstream losses. Examples of such research might be using genomic markers to locate
hot spots of denitrifier activity, evaluating the N status of forests in the basin and their
tendency to store versus export depositional N inputs, determining the rates of N fixation
by agricultural crops in the basin and the fate of that fixed N, evaluating the role of soil
health in nutrient retention and losses, evaluating the volatilization of ammonia from
manure on dairy farms in the basin, determining the potential for reducing farm-scale N
and P pollution through changes in diet fed to milk cows, investigating soil and crop
management techniques to reduce N and P input as well as leaching/runoff, for example
through tillage, organic soil management or cover crops, and studying the relationship
between water residence time and loss of N through denitrification in riparian wetlands
and first-order streams. These are given as examples only, and we have no predisposed
tendency to support a particular research topic. The criteria for funding will be the
creativity of the idea, the potential to shed new insights on fluxes of nutrients and
sediments in the Susquehanna River Basin, the opportunities to reduce these
environmental risks, and the likelihood that the project will lead to a longer term
sustained research effort. High risk projects (those unlikely to receive initial funding
from traditional funding sources, yet may have potentially large pay-offs) will be
encouraged. To maximize the ability for interested researchers to see opportunities for
coordination and collaboration on proposal, preproposals may be used to screen topics
and to develop a list of proposed projects to circulate among the Cornell community.
For the mini-grants, we envision perhaps 10 awards of $1,000 to $3,000 each. These will
be modeled after successful programs previously run at Cornell, such as the mini-grants
of the NSF-funded Research Training Grant in Biogeochemistry & Environmental
Change or the Cornell Center for the Environment. These are primarily aimed at
graduate students. For a very modest investment, we can provide substantial help to
thesis research while also directing some of the focus of student research towards the
overall objectives of this proposal: understanding the sources and sinks of nutrients and
sediments in the Susquehanna River Basin. By engaging the students, we believe we can
also increase the awareness and engagement of the Cornell faculty in this area.
Both types of grants will be awarded on a competitive basis by a committee appointed by
the PIs of this project, and each will receive peer review. The timing of calls for both
types of proposals will be coordinated to achieve both the best diversity of pertinent
research and the best overall integration of supported projects toward the program
objectives. We will encourage interaction and foster collaboration among the funded
efforts, using mechanisms such as web-based communications, list-serves, and
workshops/seminars. To develop initial interest, we intend to hold a workshop that
highlights the objectives of the overall project and the background context for nutrient
11
pollution in general and for Chesapeake Bay and the Susquehanna basin in particular.
Our web site will be designed to be used for data sharing and linking to other projects and
information relating to nutrients and sediments in the Susquehanna River basin.
Long-term research sites:
We propose to encourage field-based research at two long-term research sites, whenever
that is appropriate. This can help provide interaction among the component research
efforts, and also provides sites with detailed and current databases for calibrating and
testing our modeling efforts. The grant will augment support for these sites and compile
previous data from the sites that is pertinent to the overall project objectives. One of the
sites is a dairy farm operated by Cornell as a research and teaching center, and the other
is an atmospheric deposition monitoring station in a state forest.
Harford Teaching and Research Center:
One of the sites is Cornell’s agricultural Teaching and Research Center in Harford, NY
located in a valley varying from 1 to 3 km wide. This dairy and beef farm, owned and
operated by Cornell, is typical of those located in the upper Susquehanna River basin. It
includes approximately 526 hectares of cropland which has been in maize and alfalfa
since 1979About 390 ha are used for the dairy operation exclusively. Like many farms in
the region, the valley bottom land is intensively farmed while the steep hillsides are
forested or are in permanent grassland. The university moved into the facility in 1973,
and there are records from that time. There is a drainage divide is in the middle of the
farm, with some water going to the St. Lawrence and some to the Susquehanna. Most of
the intensively farmed land is in the Susquehanna. Most of the water drainage is ground
water in deep gravel outwash aquifers. About 40% of the ground water is from the
intensively farmed valley floor and the remainder from the surrounding hills. There are
no farming operations above the farm (the land is owned by Cornell and is woodland).
A now-retired faculty member, David Bouldin, had 15-18 wells dug on the fields at the
Harford Teaching and Research center and monitored water quality for ~ 15-20 years
before his retirement in 2000. Karl Czymmek, an Extension Associate who is part of the
Pro Dairy program at Cornell, has continued to take samples since Bouldin's retirement.
Detailed nitrate data from the wells through the year exist for at least 1979-1981 and
1992-1994, in addition to more sporadic sampling over time. There was a 2-fold increase
in nitrate from the well water between 1981 and 1994 with some variation among wells.
One well in the middle of the most intensively farmed area exceeded the permissible
level of nitrate-N (10 mg/kg). We have detailed data since the 1970s on soil test results
(pH, P, potassium, and N availability) and crop yields. The farm currently has a CAFO
plan, so that there are good records of manure and fertilizer applications that go back
about 20 years. We also have data on the amount of nutrients brought onto the farm in
the form of animal feed. The benefits of this site are clear: we have good knowledge of
cow numbers, field management, soil test results and well water measurements dating
back 20 years on a farm with soils and management characteristic of many in the region.
We propose to again intensively sample these wells (some of which need repair) over an
annual cycle (monthly sampling), and we will measure dissolved organic N and ammonia
12
in addition to nitrate. We will also begin to collect surface water samples for analysis of
nutrients and sediments from drainage creeks and streams at the site. Sampling will be at
least monthly, with an effort to also sample during storm events. We will analyze for
sediments, nitrate + nitrite, ammonium, total dissolved N, soluble reactive P, total
dissolved P, and particulate N and P, using the standard procedures of the Cornell
Nutrient Analysis Laboratory (CNAL) in the Departments of Crop & Soil Sciences and
Horticulture and the Biogeochemistry Analytical Facility in the Department of Ecology
& Evolutionary Biology. We also will begin to monitor the deposition of ammonia and
ammonium along gradients away from the farm site, using both bulk deposition
measurements (Fahey et al. 1999) and passive samplers for ammonia gas in the
atmosphere, as described in the next section.
Connecticut Hill Atmospheric Atmospheric and Precipitation Chemistry Research Site:
This site is located on a 6-hectare site within the Connecticut Hill State Forest. The site
has been in continuous operation since 1976, and is part of the National Atmospheric
Deposition Network (NADP site NY67), which measures wet deposition and monitors
trends in precipitation chemistry. Complementing this work, in 1987 the site became one
of the original locations to measure regionally representative dry deposition in the US,
and is part if the Clean Air Status and Trends Network (CASTNet site CTH 110). The
site was originally set up to study and monitor precipitation chemistry and deposition in
an area selected to be regionally representative of a large geographical area uninfluenced
by any local pollution sources such as power plants, urban centers, farms, or highways.
The site is in an area of the Susquehanna River watershed surrounded by extensive
forestlands (i.e. the 4500 ha NYS Connecticut Hill Game Management Area) as well as
old field and pasture. Both the landscape (hill and valley) and land use are typical of
other headwater sections of the Susquehanna River watershed in New York State. Thus,
this site is an ideal location to monitor and advance the understanding of the atmospheric
inputs of N and other atmospheric species influencing the Susquehanna River in New
York State. The site is managed by the Institute of Ecosystem Studies (IES), under the
direction of Gene Likens, director of the IES and adjuct professor at Cornell. The site is
run by Tom Butler, working out of the Howarth lab at Cornell.
In addition to the NADP and CASTNet monitoring, other research at the site has included
studies of throughfall versus inferentially measured dry deposition of N and sulfur
species, the initial testing and use of passive samplers as measures of dry deposition of N
species, including some not measured by CASTNet (NH3 and NO2), isotopic studies (15N,
18
O and 17O) of wet and dry deposition to understand the sources of NO3 deposition (ie
vehicle vs non-vehicle NOx emissions), and the impact of changing emissions of SO2 and
NOx on wet and dry deposition of N, sulfur and acidity. This makes it one of the best
studied sites in the country for atmospheric deposition. Nonetheless, as with other
depositional monitoring sites, some significant uncertainties remain. One of these is the
extent of dry deposition of N, particularly for gaseous N. At least 1/3 of the measured
total N deposition at the sites is in the form of dry deposition, but not all components
have yet been measured. We now propose further investigation of the use of passive
samplers as measures of dry deposition for several N species including NH3, NO2, NO
13
and HNO3 (modified samplers). Some preliminary work is being done on the spatial and
temporal variability of passive samplers (E. Boyer and C. Kendall, unpublished).
We will expand on this work to assess the comparability of passive sampler data
(concentration estimates for various N species) with the filter pack measurements
employed by the CASTNet measurements at this site. We will also test the spatial
variability of dry deposition products, since elevation, slope aspect and proximity to
roadways or other pollution sources can all impact rates of dry deposition of N, Further,
we propose the real-time measurement of gaseous NH3, and HNO3 and NOy (as well as
other atmospheric trace gases) using newly developed instrumentation that will be
deployed at selected CASTNet sites, including this one. Measurement of these species
using some of the latest instrumentation technologies will allow for the best estimates of
the true atmospheric N deposition that is impacting the Susquehanna watershed.
Calibrating the passive samplers to the results from these more detailed measurements
will increase the usefulness of passive samplers as an approach that we and others can
then use more broadly across the landscape for better estimation of spatial patterns of N
deposition. Coupled with wet deposition measurements, these approaches will give us
the best estimates of total N atmospheric deposition and the speciation of N. The
quantification of currently unmeasured species ( NH3 and NO2) and more accurate
measurements of other N species (HNO3) will result in a better understanding of the
relative importance of atmospheric N deposition.
Current Work:
Current related work includes the limited effort by the Howarth lab to apply the ReNuMa
model to the upper Susquehanna River Basin (funded with USDA Hatch funds; $15,000
per year), as well work in the Howarth lab to further develop the structure for ReNuMa
and apply it as well as the SCOPE/NANI approach across a variety of watersheds in
North America and Europe (funded through the EPA STAR program). Other related
research includes a new effort by Christy Goodale to begin to examine the status of N
saturation in the forests of the upper Susquehanna River Basin (a one year starter grant
from the USGS/Water Resources Institute for New York). Basic core support for the
Connecticut Hill deposition monitoring station continues to be provided by EPA and by
NOAA, and basic support for the Harford agricultural Research and Teaching Center is
provided by Cornell. Further, there is a great deal of work by Cornell faculty, staff, and
students on N and P dynamics at a variety of scales, from molecular to watershed.
Facilities and Equipment:
Field research facilities in addition to two core research sites described above include
numerous research farms and experimental areas in close proximity to the Cornell
campus. Controlled environment growth chambers and greenhouse space are widely
available across campus. Cornell faculty research laboratory facilities are well-equipped
with such items as UV, visible, and IR spectrophotometers, fluorometers, gas and liquid
chromatographs, as well as field sampling equipment needed for agricultural and
environmental research. Analytical facilities for nutrient analysis of soils, waters, and
biological materials by simultaneous, multi-element ICP, continuous flow autoanalyzer,
and C and N analyzer are available through the Department of Crop and Soil Sciences
14
and the Department of Ecology and Evolutionary Biology. The mass spectrometer
facility also in the Department of Ecology and Evolutionary Biology houses instruments
with dual inlet and continuous flow capabilities, coupled to a Carlo Erba CNS analyzer
for solid samples, and a Europa Geo 20-20 IRMS configured for continuous flow
measurements on bulk samples and trace N2 and CO2 measurements. This facility houses
equipment for sample preparation needs, including freeze dryers, grinders, drying ovens,
muffle furnaces, balances, and extraction prep lines. NSF-supported facilities include an
NMR center in the chemistry department and a supercomputer center with an IBM 3090600E mainframe with vector facilities and floating point system scientific computers.
Cornell has an excellent library system, including one of the best agricultural libraries in
the nation. Several micro-computing centers exist across campus; one is established
primarily for GIS work. In addition the Northeast Regional Climate Center is housed at
Cornell with historical and real-time climate data stores and information to assess the
current climate conditions and its impact on regional economic sectors.
Project Timetable:
The watershed-scale modeling and the expanded work at the Harford and Connecticut
Hill sites, described above, will begin with the start of the grant on August 15, 2005, and
will continue through the year. We will set up committees and solicit proposals for the
plot- to file- to farm-scale modeling as soon as we receive word that the proposal is
funded, and make those awards as soon as practicable to ensure optimum interaction with
the watershed-scale modeling over the year. We will set up a web site for the project in
August, and announce the project to the Cornell community through a variety of oncampus list serves at that time. We intend to hold the workshop for the project in
September. We will ask for pre-proposals for meso-scale grants in October, and solicit
full proposals (with our feedback) for the meso-size grants that will be due in November.
Mini-grants will also be due at that time. We will make awards in December, and
encourage full interaction among these components for the rest of the grant year.
Key Personnel:
The project is under the overall control of a faculty committee appointed by the College
of Agriculture and Life Sciences at Cornell, and reports to Bill Fry, Senior Associate
Dean for the College. The committee consists of Nelson Hairston (Department of
Ecology & Evolutionary Biology), Bob Howarth (Department of Ecology &
Evolutionary Biology), Johannes Lehmann (Department of Crop and Soil Sciences), and
Alice Pell (Department of Animal Sciences). The committee developed the focus for this
proposal, with principal investigators Howarth, Lehmann, Pell, and Roxanne Marino
(Department of Ecology & Evolutionary Biology). The committee and PIs will work
jointly to fulfill the goals of the project, and will have responsibility to appoint
committees for the development of further modeling activities across scales, for the
award of meso-size grants, and for award of mini-grants. Howarth will chair the overall
effort and serve as project director for the grant. He will also supervise the coordination
of the modeling efforts. Pell and Lehmann jointly will be responsible for the work at the
Harford agricultural Teaching and Research Center. Marino will be responsible for
oversight of the work at the Connecticut Hill depositional monitoring site.
15
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