Coupled biogeochemical and hydrological responses of streams and rivers to drought

Abstract

Summary Severe or extreme droughts occurred about 10% of the time over a 105‐year record from central New Mexico, U.S.A., based on the Palmer Drought Severity Index. Drought lowers water tables, creating extensive areas of groundwater recharge and fragmenting reaches of streams and rivers. Deeper groundwater inputs predominate as sources of surface flows during drought. Nutrient inputs to streams and rivers reflect the biogeochemistry of regional ground waters with longer subsurface residence times. Inputs of bioavailable dissolved organic carbon to surface waters decrease during drought, with labile carbon limitation of microbial metabolism a byproduct of drought conditions. Decreased inputs of organic forms of carbon, nitrogen and phosphorus and a decrease in the organic : inorganic ratio of nutrient inputs favours autotrophs over heterotrophs during drought. The fate of autotrophic production during drought will be strongly influenced by the structure of the aquatic food web within impacted sites.

Biodiversity, Species Interactions and Ecological Networks in a Fragmented World

“…Climate change is also to exacerbate hydrological droughts (Poff and Zimmerman, 2010) via reduced rainfall in many areas (Kundzewicz et al, 2008), potentially causing widespread habitat loss and fragmentation (Boulton, 2003;Lake, 2003;Ledger et al, 2011). During droughts, river flows decline, reducing the volume of wetted habitat (water width and depth) and altering habitat structure, increasing water temperature, reducing dissolved oxygen (Everard, 1996) and altering nutrient supply (Dahm et al, 2003). In some regions, droughts occur predictably as part of the natural hydrologic cycle and species are able to tolerate such conditions (Bonada et al, 2007), but elsewhere unpredictable drought fragmentation can have devastating effects on aquatic food webs .…”

Continental hydrosystem modelling: the concept of nested stream–aquifer interfaces

“…The hydraulic gradient defines the water pathways (Winter, 1998), whereas the geological structure defines the conductive properties of the streamaquifer interface (White, 1993;Dahm. et al, 2003).…”

The impacts of drought on freshwater ecosystems: an Australian perspective

“…Tramer, 1977;Boulton & Lake, 1992;Velasco & Millan, 1998). In pools, filamentous algae may proliferate, especially if there are high levels of nutrients in the groundwater (Dahm et al, 2003). Extended low flows can stress stream fish and lead to reduced growth and recruitment for some, but usually not all species in rivers and streams (e.g.…”

“…In some pools, especially unshaded ones, algal blooms may develop (Dahm et al, 2003). With time, conductivity may rise, high temperatures and stratification may occurall of which may severely stress the normal stream biota.…”

“…Loss of habitat, poor water quality and biotic interactions, especially predation, all have a major effect on aquatic biota and ecosystem functioning (Boulton, 2003;Dahm et al, 2003;Lake, 2003;Matthews & Marsh-Matthews, 2003;Stanley et al, 2004). Overall, the impacts of drought on population and community structure are better understood than impacts on ecosystem processes.…”