Tanners Point Environmental Monitoring Results
(February 2012)
Introduction
Many of the Bay of Plenty’s coastal communities are served by on-site wastewater treatment
systems. In areas of more concentrated dwellings located near sensitive water bodies or in areas
utilised by the public, there is the potential for adverse environmental effects from on-site treatment
systems. Adverse effects can include: odours; contamination of surface waters; addition of
nutrients to water bodies; contamination of shellfish and foreshore environments; and negative
health effects of water body users.
What Environment Bay of Plenty Monitor
Methods employed to detect contamination in the environment involve surveying surface waters
(drains, seepages, streams etc.) and groundwaters and using analytical and microbiological
techniques to determine contaminant concentrations and/or loadings. Water samples are
commonly analysed for nitrogen and indicator bacteria (Escherichia coli (E.coli), faecal coliform,
and enterococci). Similarly, lake or harbour waters are also monitored for indicator bacteria as a
potential symptom of contamination.
What do the results tell us?
Nitrogen, particularly in its ammonia form (NH4) and to a lesser extent in its oxidised form, nitrate –
nitrite-nitrogen (NNN) is used to help detect the presence of septage in water. Elevated results
can indicate sewage contamination.
Micro-organisms such as bacteria, protozoa and viruses can be removed from septic tank effluent
in the top soil layers, dependant on soil pH, moisture, temperature, and soil microbial population. If
effluent comes in contact with a saturated zone (e.g. elevated water table) connected to surface
then faecal micro-organisms and pathogens can be readily transported into the environment.
Elevated results of these indicators or the presence of them in shellfish can indicate a
contamination problem. Bacterial contamination may have human or animal origin.
Monitoring Sites
Refer to the map at the end of this report.
Results
The Tanners Point boat ramp area provides most of the focus for monitoring. This area has a
permanently flowing drain and a small seepage at the harbours edge, as well as several
subsurface drains that flow into a water table drain located at the landward side of the reserve.
Moana Drive also has an ephemeral stormwater drain that flows towards the northern beach.
The permanently flowing drain adjacent to the boat ramp at Tanners Point has been the most often
sampled flow on the peninsula. Figure 1 shows that the drain has faecal coliform and enterococci
concentrations have on average been improving since 2007. Median E.coli levels have also been
monitored and are for the same 2007-2011 period well under the contact recreational limit of 550
cfu/100ml (red alert mode, orange alert mode is E.coli > 280 cfu/100ml).
NNN results are also high, indicating that septic tank contamination is likely to be occurring, but
that much of the ammonium is being converted to NNN. High NNN results have also been found in
the waters emanating from the sub-surface drains Ammonium-nitrogen and dissolved reactive
phosphorous concentrations also have at times been at levels that suggest a contamination
source.
Boat Ramp drain
10000
Ent erococci (cfu/100ml)
1000
100
10
1
10/10/06
22/02/08
06/07/09
18/11/10
01/04/12
Boat Ramp drain
0.3
0.25
NH4-N (g/m3)
0.2
0.15
0.1
0.05
0
10/10/06
22/02/08
Figure 1
06/07/09
18/11/10
01/04/12
Indicator bacteria and dissolved nitrogen concentrations, Boat Ramp drain,
Tanner Point.
Figure 2 displays data for Boat Ramp drain along with two other smaller drains that flow
onto the foreshore. Both the other drains display similar, if not at times higher, levels of
nutrient and indicator bacteria. E.coli concentrations have of late improved in all drains,
although enterococci levels were elevated in both Drain #2 and Moana Drain in April
2011. Ammonium levels were not excessive at this time and elevated enterococci may be
from a vegetative source.
Dissolved nutrient also show general improvement with the exception of nitrate–nitritenitrogen which continues to show elevated results, particularly from Drain #2.
Tanner Point Drains
0.4
0.35
0.3
DRP (g/m3)
0.25
0.2
0.15
0.1
0.05
0
10/06
04/07
11/07
06/08
12/08
07/09
01/10
08/10
02/11
09/11
04/12
Boat ramp drain
Figure 2
Drain #2
Faecal coliform and nutrient concentrations, Boat Ramp drain, Tanner
Point.
Bathing surveillance monitoring undertaken at the boat ramp for this summer has only
recorded one value over the microbiological water quality guidelines (2003) in eight
seasons. This exceedance may have been the result of an illegal boat discharge, flow
from the Tuapiro River or water fowl rather than a land based discharge from Tanner
Point.
Figure 3
Bathing surveillance monitoring, Tanner Point Jetty.