Phosphorus and Nitrogen

Phosphorus How is P used in organisms? Biomolecules ADP and ATP nucleic acids phospholipids (cell membranes) apatite (bones and tooth enamel)

Forms of Phosphorus Phosphorus in aquatic systems is usually categorized how we measure it. Dissolved P = Any P that goes through a 0.45um filter PO 4 3- polyphosphates Dissolved organic phosphates Particulate P = Any P that is retained on the filter in algae, zooplankton, detritus, attached to sediment particles. Total P = Dissolved P + Particulate P Reactive P = P that reacts with molybdenum to form a blue color. The most commonly measured forms of P are Total Phosphorus (TP) and Dissolved Reactive Phosphorus (DRP)

Limiting nutrients Theoretically, phosphorus is usually the most limiting nutrient in freshwater systems as determined by Liebig’s Law of the Minimum and Ecological stoichiometry

Liebig’ Law Growth is limited by the nutrient that is in shortest supply. P N FeC

Limiting nutrients Ecological stoichiometry Ratios of elements in plankton and other organisms Important in addition to Liebig’s law

Stoichiometry gives the “recipe” for phytoplankton Cake Example 2 1/4 cups sifted cake flour 2 teaspoons baking powder 1/2 teaspoon salt 1/2 pound Butter 2 cups sugar 4 large egg yolks 2 teaspoons vanilla 1 cup sour cream 4 large egg whites

Recipe for phytoplankton is the Redfield Ratio In the 1950s Alfred Redfield found in the deep ocean an average phytoplankton composition (by number of atoms) of C H O N P S Fe Note that C, H, O, and N are required in greater proportion than P. Why then are these NOT the generally nutrient limiting?

In freshwater systems P is usually limiting because the amount of P available to primary producers is much less than the amount required relative to the other elements. P makes up only ~1% of organic matter which implies that if nothing else is limiting, then increasing P can theoretically generate >100X the weight of added P in algae C H O N P S Fe

2 1/4 cups sifted cake flour 2 teaspoons baking powder 1/2 teaspoon salt 1/2 pound Butter 2 cups sugar 4 large egg yolks 2 teaspoons vanilla 1 cup sour cream 4 large egg whites Suppose you were a baker and wanted to sabotage a rival baker by stealing supplies from his storehouse. You can carry 50 lbs. of any ingredient with you. What do you steal in order to prevent him from making the most cakes? The Burglar Baker

2 1/4 cups sifted cake flour 2 teaspoons baking powder 1/2 teaspoon salt 1/2 pound Butter 2 cups sugar 4 large egg yolks 2 teaspoons vanilla 1 cup sour cream 4 large egg whites i.e. If you have plenty of everything else, then with only ½ teaspoon of salt, you can bake a cake.

Phosphorus and Lake Classification The productivity of a lake is often determined by its P loading and its volume (mean depth)

Lake Productivity Classification Total Phosphorus  g/L Ultra-oligotrophic <5 Oligotrophic5-10 Mesotrophic10-30 Eutrophic Hypereutrophic >100

Sources of Phosphorus Weathering of calcium phosphate minerals, especially apatite [Ca5(PO4)3OH] from sediments of ancient oceans. There are no important gaseous sources of P. Anthropogenic P is now often much greater than natural inputs of P in many watersheds Sewage, agriculture, etc.

Sources of Phosphorus Increased production of algae due to increased Anthropogenic P input is cultural eutrophication Anthropogenic P may come from point sources (think of a pipe) nonpoint sources (diffuse, like agriculture runoff)

Point and Nonpoint sources thinkquest.org

External vs. Internal P Loading “Loading” refers to input of a nutrient per unit time Usually calculated for rivers as concentration x flow External loading refers to sources outside the lake (as in previous slide) If all external sources of P were removed, a lake would continue to grow algae for many years. This is because P is recycled within the lake. This recycling is termed Internal Loading

Lake sediments can trap P under oxic conditions or release P under anoxic conditions P diffusion Diffusion Barrier Oxygen profile of sediments in oxic conditions

Internal P Loading P may be recycled in the food web several times Phytoplankton are extemely efficient at absorbing any P that is released by excretion or decomposition Eventually P will be lost from lake either by outflow or by sedimentation to the lake bottom. P is bound in lake sediments under oxic conditions, but may be regenerated from sediments under anoxic conditions (iron and microbes play an important role) P may be recycled in the food web several times Phytoplankton are extemely efficient at absorbing any P that is released by excretion or decomposition Eventually P will be lost from lake either by outflow or by sedimentation to the lake bottom. P is bound in lake sediments under oxic conditions, but may be regenerated from sediments under anoxic conditions (iron and microbes play an important role) lakes.chebucto.org/DATA/PARAMETERS/TP/popup.html

Internal P Loading Deep lakes with oxic hypolimnia and long WRT may retain 70-90% of incoming P in the sediments Lakes with Anoxic hypolimnia retain only half as much P as lakes with oxic hypolimnia Therefore external loading may result in a positive feedback loop that amplifies eutrophication. Deep lakes with oxic hypolimnia and long WRT may retain 70-90% of incoming P in the sediments Lakes with Anoxic hypolimnia retain only half as much P as lakes with oxic hypolimnia Therefore external loading may result in a positive feedback loop that amplifies eutrophication. lakes.chebucto.org/DATA/PARAMETERS/TP/popup.html

 phytoplankton  decomposition  hypoxia  regeneration of P from sediments  external P loading Positive Feedback Loop

Bioturbation Physical re - suspension by organisms living in oxic sediments may also increase the regeneration of Phosphorus from sediments into the overlying water J. Chaffin Without Mayflies With Mayflies

Phosphorus Remediation Eutrophication can be ugly: high algal biomass (sometimes toxic), hypoxia, fish kills, foul smells One answer is to reduce P loading by Removing P from waste water (tertiary treatment) Diverting waste water (see Lake Washington) Using natural or constructed wetlands to trap P Using buffer strips to trap agricultural runoff Using pumps to aerate the hypolimnion

Wastewater Treatment Addition of alum to precipitate P

Buffer Strips NRCS

content.cdlib.org/xtf/data Hypolimnion Aeration

The importance of the Maumee River watershed in phosphorus loading to Lake Erie

D. Dolan, LEMN conf. 2010

A look at P in the Maumee River (from P. Richards and D. Baker, NCWQR) Study completed in 1995 showed almost all trends improving, now they are getting worse.

Both river flow and DRP concentration have increased, therefore much greater DRP loading

The Maumee River watershed is causing a high degree of stress to Lake Erie J. Kelly, LEMN Conf. 2010

Where is the dissolved P coming from? Investigation by the Ohio Phosphorus Task Force Agriculture Conservation Tillage Reduces soil erosion, but… Fertilizer remains near the soil surface and is more easily washed into tributaries

Stratification of P in soils

Conservation Tillage may have unintentional side effects

Where is the dissolved P coming from? Investigation by the Ohio Phosphorus Task Force Agriculture Conservation Tillage Fertilizer is not incorporated into the soil and is more easily washed into tributaries Fall application of fertilizers Continuation of old P-building practice CAFOS (concentrated animal feeding operations) Produce large amounts of animal waste with poor waste treatment practices Municipalities Combined sewer overflows (CSOs) Addition of P to water supply as anti-corrosive See Ohio Lake Erie Phosphorus Task Force Final Report ptaskforce/Task_Force_Final_Report_April_20 10.pdf ptaskforce/Task_Force_Final_Report_April_20 10.pdf

The Microcystis-Anabaena bloom of 2009 was the largest in recent years in our sampling region The Microcystis-Anabaena bloom of 2009 was the largest in recent years in our sampling region 2011 …until 2011 …until 2011

Phosphorus loading is important, but what about Nitrogen? Phosphorus remains high throughout the growing season. Nitrogen loading and concentration drop during the summer, leading to Nitrogen- limited conditions.