Eutrophication 2.1 Biogeochemical cycles Alice Newton P. Viaroli

Important nutrients N:P:Si ~ Ratios N:P and N: Si are especially important ~ N is usually limiting nutrient in coastal waters and estuaries. Can be fixed by cyanobacteria ~ P most important in freshwater lakes. Anoxic sediments release P ~ Si important for phytoplankton composition (diatoms)

Redfield ratio N:P 16:1 ~ N limited when <16:1 ~ P limited when >16:1 ~ Range of 10 to 25 is “normal” ~ N:P in sewage, manure and fertilizers is different from Redfield ratio.

N:Si 1:1 ~ Upstream eutrophication in rivers traps Si in sediments before it reaches estuaries ~ Dams: trap Si ~ Si availability controls diatom growth ~ Decrease in Si relative to N & P linked to changes in phytoplankton community and HABs

Nitrogen cycle

(red-ox) N-cycle Biochemical pathways AnAmOx nitrification Dissimilative Nitrate Reduction to Ammonium denitrification Assimilative reduction N-fix A AR P. Viaroli

Nitrification total: NH O 2  NO H 2 O+ 2H + Nitrification1: NH O 2  NH 2 OH + H + NH 2 OH + O 2  NO H 2 O + H + Nitrification2: NO O 2  NO 3 - Nitrogen fixation N 2 +6e - + 6H +  2NH 3 Denitrification (+OM, -O 2 ) Nitrification (+O 2 ) P. Viaroli Ammonium-ammonia equilibrium NH 3 + H 3 O +  NH H 2 O pKa = 4.75

NH 4 + NO 2 - NO 3 - N2N2 N - phytoplankton N in zooplankton N-fish N-detrital N - sedimentary Nitrogen cycling in pelagic waters (plankton-dominated) P. Viaroli N in benthos (zoo and phyto)

Biology of N ~ Gaseous N 2 not useful to most photosynthesizers ~ N fixation ~ eg Trichodesmium can produce NH 4 from N 2 ~ Microbes and BG algae may form NO 2 and NO 3 ~ NH 4, NO 2 and NO 3 can be used as nutrients by photosynthesizers ~ Proteins in Organic matter are excreted or decompose as NH 4

N org. NH 4 + NO Nitrification Nitrosomonas, Nitrobacter N 2 ONO N 2 Ammonification Denitrification Pseudomonas,Thiobacillus Anoxic horizon oxic horizon water DNRA Atmosphere N 2 Nitrogen fixation Cyanobacteria P. Viaroli N-cycle in shallow waters

dark light Denitrification (mmol m -2 h -1 ) in a Ruppia meadow Denitrification from water nitrate Coupled nitrification-denitrification

light dark Denitrification rates determined with dark and light incubations

Quantifying the N cycle ~ N cycle: ~ Natural Sources of N ~ Anthropogenic sources Natural Sources ~ Lightening fixation 5-10Tg pa ~ Natural N fixation (non crop) Tg p.a. ~ Marine fixation Tg pa??? (Teragrams = 1 million metric tonnes)

Anthropogenic sources of N ~ Industrial fixation inc Fertilizer 80Tg of N pa (NH 3 & N 2 O) 2020 projection 134 Tg pa ~ Agricultural Legume Fixation Tg pa ~ Fossil fuels 20 Tg pa (NO & NH 3 ) 2020 projection 46Tg pa ~ Forests Burning 40 Tg pa (NO, N 2 O & NH 3 ) ~ Loss of wetlands (denitrifying) 10 Tg pa ~ Land clearing for crops 20 Tg pa ~ Domestic and Animal Waste 32 Tg pa (NH 3 ) 1996 Total annual anthropogenic N inputs ~140Tg (Teragrams = 1 million metric tonnes) see text below

Human alteration to N cycle ~ N has doubled in 50 years (C has only increased 10%) ~ 80 Tg of N pa applied as fertilizer ~ 174 kg/ha/pa Xs ~ Impacts include: ~ Increase N 2 O, (nitrous oxide, a greenhouse gas), due to burning of fossil fuels ~ Increased NO (nitric oxide, photochemical smog formation) ~ Acidification of soils and freshwater ~ Erosion & leaching of N to estuaries and coast (Teragrams = 1 million metric tonnes)

Changes in N cycle Revised Kates et al. (1990).

Human-Caused Global N- Emissions

Atmospheric deposition

NOx and NHx in the Atmosphere Origins ~ Domestic combustion ~ Industrial processes ~ Traffic ~ Agricultural sources ~ Animal housing ~ Spreading of manure

A tmospheric D eposition of N in the N orth A tlantic O cean ~ AD-N to the NAO basin arises from pollution sources in North America and Western Europe ~ Sources have increased drastically (5-10-fold) since the Industrial Revolution and continue to increase in both geographic and depositional magnitude. ~ AD-N flux (11.2 Tg N yr -1 ) accounts for 46-57% of the total "new" or anthropogenic nitrogen flux to the NAO. (Teragrams = 1 million metric tonnes)

Transfers of nitrogen ~ N fixed in industrial areas ~ N transported to agricultural areas ~ N applied to fields, some retained in crops ~ N loss to atmosphere and water ~ Crops transported to livestock producing areas and cities ~ Crops consumed in cities and N enters sewage ~ Animal feed crops consumed in livestock farms ~ Livestock transported to cities ~ Manure spread on fields, enters atmosphere and water

Industrial areas Agricultural areas Atmosphere Aquatic environment Livestock area Cities

Natural transfers ~ Sea Birds and guano ~ Salmon migration and death

N input into Aquatic Systems Modified from Howarth et al. (1996)

NO 3 in major EU rivers Nitrate concentrations have been largely unchanged since 1980 EEA

NO 3 in EU coastal waters

P-Cycle ~ P most important in freshwater lakes ~ P limitation has been documented in coastal waters and estuaries: ~ Apalachicola (Gulf of Florida) ~ some Dutch estuaries ~ Tropical systems with carbonate sands ~ P is released from anoxic sediments ~ N-fixing cyanobacteria proliferate when P is abundant, e.g. in the Baltic sea

P-Cycle P.Viaroli

Primary producers P-Refractory External load burial/early diagenesis PO 4 Clay Fe  P Ad-sorption De-sorption Assimilation Decomposition Organic Detritus Precipitation (es:apatite, hydroxiapatite) Assimilation Ca  P P-cycle P. Viaroli

Human alteration to P cycle ~ 600 Tg applied as fertilizer from 1950 to 1995 ~ ~250 Tg of P harvested as crops ~ ~50 Tg used as feed crops returned to soil as manure ~ Net XS addition 400 Tg in 45 years, ~10 Tg p.a. (Teragrams = 1 million metric tonnes)

Sources of P in EU

P sources in the UK EA UK

P in major EU rivers Phosphorus concentrations in some EU rivers have fallen since the mid-1980s, particularly in the largest and most polluted rivers. EEA.

P in coastal waters EEA

NO3 & PO4 in EU coastal waters, Nutrient concentrations in coastal waters show little overall improvement