Stream Ecology (NR 280) Topic 11 – Nutrient Dynamics Nutrient Cycles and Budgets Nutrient Transport, Spiraling and Uptake Controls on Nutrient Dynamics Measuring nutrient uptake

General definitions Nutrient Cycle – depicts the processes by which a nutrient moves through the environment – Typically, not quantitative – Has no particular scale in time or space Nutrient Budget – depicts the amount of nutrient held in pools and transferred in fluxes – Typically, quantitative – Usually specific to a scale in time and space

Common Terms Pools – real or conceptual reservoirs that hold particular forms of a nutrient Fluxes – rates at which nutrients are transferred from one pool to another Steady state – a unique condition in which contents of all pools in a budget remain constant because the sum of inputs to each pool is equivalent to the sum of outputs from each pool

Mass units in budgets UnitAmountNameAlternate ng10 -9 nanogram μgμg10 -6 microgram mg10 -3 milligram g10 0 gram Kg10 3 kilogram Mg10 6 megagrammetric ton (tonne) Gg10 9 gigagram Tg10 12 teragrammegaton(ne) Pg10 15 petagramgigaton(ne) Mass of all vegetation on earth is ~560 gigatons

Common Units at the Global Scale 1 Tg = 1 Teragram = grams Equivalent to… 1Mt = 1 Megaton = 10 6 tons = 10 9 kilograms = grams 1 Pg = 1 Petagram = grams Equivalent to… 1 Gt = 1 Gigaton = 10 9 tons = kilograms = grams

The Carbon Cycle Carbon Dioxide CO 2 Autotrophs Aerobic Heterotrophs Detritus Methane CH 4 Photosynthesis Herbivory Detritivory Death Methane Oxidation Respiration Fermentation Sunlight Oxygen Energy Oxygen Energy Methanogenesis +Oxygen -Oxygen Anaerobic Heterotrophs Energy Non-oxygen TEAs Micro/Macro Predation Competition etc.

The Global Carbon Budget petagrams per year

Global Carbon Budget (1990’s) Houghton (2007) Note: “~” not “-” on values Arctic

Arctic Carbon Budget McGuire et al. (2010) What happens if these increase?

Arctic Carbon Budget McGuire et al. (2009 and 2010) 805 Pg CO 2 -C <4 Pg CH 4 -C <1 Pg CO-C

The Nitrogen Cycle A basic representation Organic N Living Dead Ammonium NH 4 + Nitrite NO 2 - Nitrate NO 3 - Nitrogen N 2 NO 2 NO N2ON2O denitrification nitrogen fixation uptake mineralization nitrification (1) nitrification (2) oxygen energy, H+ oxygen energy -oxygen +oxygen

What is happening here?

In-stream processing is important Bernhardt et al. (2005)

The Nitrogen Cycle A Stream Perspective Fig Allan and Castillo (2007)

The Nitrogen Budget – 1890 vs 1990 A Global Perspective (Units = TgN/yr) Steffen (2010)

The Phosphorus Cycle Smil (2000) Rocks Soil Inorganic PO 4 3- Biomass P Weathering Uptake Mineralization Burial Note: There is no volatile or gaseous form of phosphorus

The Phosphorus Cycle A Streams Perspective Mainstone and Parr (2002) in Allan and Castillo (2007)

The Phosphorus Budget A global perspective

Why such a focus on C/N/P? Critical functions in all biota – Carbon: backbone of all “organics”, energy – Nitrogen: key element in protein (amino acids) – Phosphorus: DNA, ATP – Oxygen: regulates processes that form the others The element cycles are tightly inter-connected – To build biomass requires CNP in correct proportion – To use biomass require CNP in correct proportion – Ecological stoichiometry (Redfield’s Ratio)

Ecological Stoichiometry Redfield’s Ratio In Sterner and Elser (2002)

Element Ratios in Nature Elser and Hassett (1994) in Sterner and Elser (2002)

We now know where the major elements come from and how they are processed in ecological systems, including streams. What factors influence the way that nutrients are processed in streams?

Nutrient Transport at the Ecosystem Level Uptake rate (U): the rate at which nutrients are taken up (disappear) from the water column Spiraling length (S w ): the distance an average molecule travels in the water column before it is taken up Units = mass/area/time (e.g. mmoles m -2 d -1 ) Units = length (e.g., m or km)

Nutrient Spiraling Newbold and Petts (1992) Originally described by Newbold et al. (1981)

Newbold’s nutrient “spiraling” concept Open-channel Transport Uptake Length (S W ) Turnover Length (S B ) Spiral Length (S) Benthic Transport Regeneration Uptake Regeneration Open-channel Transport Benthic Transport Flow NOTE: S W >> S B

Why does spiraling length decrease after a flash flood in this desert stream? In Allan and Castillo (2007)

Other influences on nutrient dynamics in streams

Influence of concentration on uptake Bio-chemical Concentration of nutrient (substrate) Uptake Rate (V) Ks Half V max V max Michaelis-Menton Uptake Kinetics

Influences on nutrient dynamics in streams H ydrological-biological Peterson et al. (2002). Also in Allan and Castill0 (2007)

Influences on nutrient dynamics in streams Effect of oxygen on P regeneration

Influences on nutrient dynamics in streams Trophic Why? Think Redfield Ratio

Influences on nutrient dynamics in streams Human

Land use affects NO 3 concentrations and uptake rate ENSC 160 Fate and Transport - Water Mulholland et al. (2009)

NO 3 uptake and denitrification rate are related to NO 3 concentrations Mulholland et al. (2009)

Land use affects stream denitrification Stream denitrification is important Mulholland et al. (2009)