Landscape exports of phosphorus and their effects on aquatic ecosystems Val H. Smith Department of Ecology and Evolutionary Biology University of Kansas Lawrence, KS USA

Eutrophication of Surface Waters by Excess Nutrient Inputs Accounts for ca. 50% of impaired lake surface area and ca. 60% of impaired river reaches in the U.S. alone Eutrophication degrades water quality in – Streams and rivers – Lakes and reservoirs – Estuaries and coastal marine waters

Lake Winnepeg photo courtesy D.W. Schindler Eutrophication is driven by excess exports of growth-limiting nutrients (N and P) from the watershed to receiving waters

Regional (watershed) scale Food, Fiber, and Biofuel production

Trophic state terminology Oligotrophic – low nutrients and low productivity; usually high water clarity Modified from: Water on the Web Eutrophic – high nutrients and productivity; very green, low clarity Mesotrophic – moderate nutrients and productivity; intermediate water clarity

Poikane et al. 2014; bio.rutgers.edu; Eutrophication trends Ultra-oligotrophic Oligotrophic Mesotrophic Eutrophic Hypertrophic

Modified from: An oligotrophic system (low in nutrients, low algal abundance)

Excess algal growth is due to high nutrient inputs Modified from: A eutrophic system (high in nutrients, high algal abundance)

Decomposing phytoplankton consume dissolved oxygen O2O2 O2O2 O2O2 Modified from:

Low or zero oxygen Oxygen depletion can cause fish kills Low or zero oxygen Modified from: Photos from:

Modified from Poikane et al Eutrophication trends Probability of Harmful Algal Blooms 100% 0%

Harmful Algal Blooms (HABs) Source: Karl Havens

Algal blooms can lead to taste and odor problems in domestic water supplies Saginaw Bay, Lake Michigan (USA)

Cyanobacterial resurgence in Lake Erie (Great Lakes): Combined effect of eutrophication and warming? Courtesy NOAA/NESDIS & NASA/SeaWiFS Microcystis spp. Lake Erie

Microcystis is a toxic blue-green alga Modified from:

Neurotoxins Chemical Structure – Alkaloids Mode of Action – Neuron ion channel blocker Symptoms – Convulsions, muscle cramps, respiratory distress, heart failure. Death can be in minutes. Occurrence – Relatively rare compared to hepatotoxins

Anatoxin-a Associated species – Anabaena flos-aquae Oscillatoria formosa Aphanizomenon flos-aquae One of first cyanobacterial neurotoxins described – ‘very fast death factor’, (Gorham 1964)

Saxitoxin Associated species – Anabaena flos-aquae Aphanizomenon flos-aquae Alexandrium sp. Gymnodinium sp. Causes paralytic shellfish poisoning. Saxitoxin is 1,000 times more toxic than nerve gas.

Hepatotoxins Chemical Structure – cyclic peptides Mode of Action – protein synthesis inhibition, cytoskeleton disruption in liver cells Symptoms – liver cancer and chronic gastro- intestinal problems Occurrence – relatively common in lakes with dense blooms of Microcystis

Microcystin One of first cyanotoxins described – ‘fast death factor’, (Bishop et al. 1959) Cyclic peptide, >50 variants Specific modes of action – necrosis of the liver, death from hemorrhagic shock. Inhibition of protein synthesis, DNA damage. Possible tumor promotion. Associated species – Microcystis aeruginosa

What Can Be Done?

We have a very sound scientific understanding of the process and the control of eutrophication Eutrophication can be reversed by decreasing external inputs of N and P, although some water bodies may exhibit variable rates and degrees of recovery.

Generalized conceptual framework for controlling eutrophication Nutrient loading to the system Total nutrient concentrations in the water column Community- and ecosystem-level responses Depends upon ecosystem characteristics (e.g., size, hydraulic residence time, and internal loading) Moderated by physical, chemical, and biological characteristics (e.g., temperature, turbidity, flushing, salinity, and food web structure)

Water quality variable N or P in water User-defined Threshold Water Quality value User-defined Threshold Nutrient Concentration in Water Column

summer spring Whole lake water microcystins in 50 New Hampshire lakes, 1999

Water quality variable N or P in water N or P loading Critical Load Required to Maintain Acceptable Water Quality User-defined Threshold Water Quality value User-defined Threshold Nutrient Concentration in Water Column

Mass balance modeling approach Areal P load = external P load/surface area: L p = TP in / A, mg P m -2 y -1 Hydraulic residence time: t w = volume/annual water load = V / Q in, yr Predicted TP = L p / (z/t w ) * 1 / (1 + sqrt(t w )) Mean depth z = V / A, meters

Science of the Total Environment 409: 1739–1745 (2011) “Traditionally, phosphorus (P) input reductions have been prescribed to control CyanoHABs, because P limitation is widespread and some CyanoHABs can fix atmospheric nitrogen (N 2 ) to satisfy their nitrogen (N) requirements. However, eutrophying systems are increasingly plagued with non N 2 fixing CyanoHABs that are N and P co-limited or even N limited. In many of these systems N loads are increasing faster than P loads. Therefore N and P input constraints are likely needed for long-term CyanoHAB control in such systems.”

Acknowledgements Jim Elser and Helen Rowe Philippe Hinsinger and the PSP5 organizers Hans Paerl Andrew Sharpley