Ecosystem implications of long-term changes in precipitation chemistry

LTER Science Council14 May 2015

Steve Hamilton, Merryl AlberCharley Driscoll, Emma Rosi-Marshall, Emily Stanley, Will

Wieder

Background• Acid precipitation has been diminishing in many parts

of the US since 1980• Sulfate seems to be the most reliable indicator of

stream and lake response– Nitrate and ammonium are subject to many influences

• Myriad ramifications for soil and water biogeochemistry, such as:– Mineral weathering and solute export– N vs. Ca limitation– Al toxicity– Hg cycling– DOC and DON export

Background• Other changes in precipitation chemistry may

also be also occurring…– Base cation increases in drier western climates

(dust?)– Urbanized areas have many local pollution sources

(P, metals, etc.) that may be increasing or decreasing

– Ammonia deposition (wet and dry) may be increasing in some places (esp. from livestock sources)

Hypothesis

• Surface waters will track changes in precipitation chemistry unless:– Large hydrological time lag (groundwater)– Large mineral weathering buffer (e.g., calcareous

geology)– Ameliorating influence of wetland flow paths

(anaerobic metabolism consumes nitrate and sulfate, but wetlands also contribute organic acids)

– Land use practices obscure trends (e.g., fertilizers, liming, etc.)

• LTER sites span the gradient of these conditions

Approach

• Propose ASM workshop• Determine data availability• Assemble and compare time series of

precipitation vs. stream chemistry• Look for trends, time lags• How far do patterns extend downstream in

river systems?• Synthesis paper is the hopeful outcome

Data needs

• Precipitation chemistry (NADP/NTN sites)• Stream chemistry: pH, sulfate, nitrate, ANC, DOC,

other major solutes– EcoTrends analysis of surface water chemistry

could be updated– Perhaps 1/3 of LTER sites have full data– USGS (mostly larger rivers, more pollution

influence)– Other monitoring programs

• Consider other surface waters where relevant

• (While we’re at it, let’s all make Gibbs diagrams for LTER sites!)