Surface Water 4

nutrients

nitrogen (coastal) and phosophorus (freshwater) are limiting for plants in aquatic ecosystems

with different biogeochemical cycles their management is very different

nitrogen cycle

gaseous and dissolved phases imp - microbial processes most important

abundant but not available, some fixing occurs but its costly

ammonium and nitrate are available for uptake

key processes include ammonification, nitrification, denitrification

ammonification

decomp of organic matter and release of ammonium NH4+

doesnt move with water as consistently

when associated with wastewater can have high and toxic concentrations

nitrification

aerobic microbial transformation of ammonium to nitrate by bacteria (NO3-)

nitrate is highly mobile in soils and move with water - so can contaminate groundwater and runoff

denitrification

NO3 to N2 or N2o

anaerobic process which leads to nitrogen removal

occurs in hyporheic zone, lake sediment and wetlands

phosphorous cycle

no gaseous phase, found as a salt and released as phosphate which is strongly fixed to mineral particles and unavailable to plants

transported with erosion, adsorbed to mineral particles

highest availability at 6.5 pH

anoxic conditions may release

cycling and reuse of phosphorus in lakes with anaerobic low pH sediments

eutrophication

naturally occurs over time, but culturally occurs when human land use adds nutrients

ag is main diffuse source, with phosphorous main issue (often from TSS)

leads to anoxic conditions, turbid water, loss of biodiversity, smell, blue green algae → phosphorous may be released in anoxic conditions leading to cycle

oligotrophic lakes

low nutrients and low productivity, usually high water clarity

mesotrophic lakes

moderate nutrients and productivity intermediate water clarity

eutrophic lakes

high nutrients and productivity, very green, low clarity

eutrophication in Ab lakes

naturally shallow and nutrient rich due to sedimentary bedrock

cultural eutrophication make algal blooms more common