1. Freshwater, Marine and
Brackish Water Resources
2. Freshwater pollution
Learning Outcomes
• At the end of this section, the students will
be able to
– describe difference between different types of
water resources
– Identify different sources of freshwater
pollution
Water class
Electrical
conductivity
dS/m
Salt
Type of water
concentration
mg/l
Non-saline
<0.7
<500
Drinking and
irrigation water
500-1500
Irrigation water
Slightly saline 0.7 - 2
Moderately saline
2 – 10
1500-7000
Primary drainage
water and
groundwater
Highly saline
10-25
7000-15 000
Secondary
drainage water
and groundwater
Very highly saline
25 – 45
15000-35000
Very saline
groundwater
Brine
>45
>45 000
Seawater
• Freshwater
– bodies of water such as ponds, lakes, rivers
and streams containing low concentrations of
dissolved salts and other total dissolved
solids. In other words, the term
excludes seawater and brackish water.
– an important renewable resource
– lakes and ponds, rivers, underground
water and man-made freshwater bodies, such
as canals, ditches and reservoirs.
• Freshwater is defined
– water with < 0.5 ppt dissolved salts
• Water salinity based on dissolved salts in
parts per thousand (ppt)
– Freshwater < 0.5
– Brackish water 0.5 – 35
– Saline water 35 – 50
– Brine > 50
• Groundwater
– water located beneath the ground surface
in soil pore spaces and in aquifers
• Aquifer
– a layer of relatively porous substrate that contains
and transmits groundwater
– Unconfined Aquifer - water can flow directly between
the surface and the saturated zone
– upper level of saturated layer of an unconfined aquifer
is - water table
– Confined aquifer - aquifer overlain by a relatively
impermeable layer of rock or substrate
Problems faced by groundwater
utilization
• Overdraft
– lowering of water table beyond the reach of existing wells
– extraction of groundwater linked to a river system affects river
flows
• Subsidence
– hydraulic pressure of groundwater and aquitard (substrate with
relatively low porosity that permits limited transmission of
groundwater) supports some of weight of overlying sediments
– by excessive pumping, pore pressures in the aquifer drop and
compression of the aquifer causing land subsidence, a drop in
the ground surface
– New Orleans, San Jose, Bangkok
• Seawater intrusion
– recharge zone of an aquifer near the seacoast
is likely to be inland
– a lowered water table may induce sea
water to reverse the flow toward the sea
– Sea water moving inland is saltwater intrusion
• Flood mitigation, infrastructure built on
floodplains – reduced aquifer recharge
Brackish water
• result from mixing of seawater with fresh
water, as in estuaries, or it may occur in
brackish fossil aquifers
• Brackish water habitats
– Estuaries, mangroves, brackish seas and
lakes
–
Uses
– Desalination for drinking
– Aquaculture
– In irrigation – moderately salt tolerant/tolerant
crops
– Industrial – cooling
Saline water
– three categories
• Slightly saline water - 1,000 to 3,000 ppm
• Moderately saline water - 3,000 to 10,000 ppm
• Highly saline water - 10,000 to 35,000 ppm of salt
– Seawater - roughly 35,000 ppm (= 35 g/L)
Causes of Saline water
• Water in rock formations that occurred in marine
conditions
• Weathering of salts from rock strata with
naturally high salt content leads to salts moving
into aquifers
• Discharge of irrigation return flows
• accelerated groundwater seepage to surface
systems
• discharges of domestic and industrial
wastewater
• intrusion of seawater into coastal aquifers
• Over extraction of the freshwater
• Use of Saline water
– desalination for drinking – heated wastewater in the
cooling process and brine disposal issues
– agriculture – crop production, aquaculture, forage
production,
– in thermoelectric-power industry to cool electricitygenerating equipment
– mining and other industrial purposes
– used extensively to irrigate gardens, parks and sports
fields
– biomass production
– salt extraction
• Water Pollution
– contamination of water bodies such
as lakes, rivers, oceans, and groundwater
– impaired by anthropogenic contaminants and
either does not support a human use (like
serving as drinking water, irrigation water etc.)
or limits the support of biotic communities
• Primary sources of water pollution grouped into
two
– Point-source pollution
• refers to contaminants that enter a waterway through a
discrete "point source“ i.e. discharges from a wastewater
treatment plant, outfalls from a factory, leaking underground
tanks, etc.
– Non-point source pollution
• contamination that does not originate from a single discrete
source
• cumulative effect of small amounts of contaminants gathered
from a large area i.e nutrient runoff in storm water from sheet
flow over an agricultural field