Impacts of droughts and low flows on estuarine water quality and benthic fauna

Abstract

The effects of droughts on benthic infaunal communities and three epifaunal species were determined in three semi-arid central Texas estuaries with different inflow dynamics and consequent salinity regimes: the Nueces, Lavaca-Colorado, and Guadalupe Estuaries. Periods (months or years) were considered to be in drought if mean salinities were in the upper quartile of historic salinities. This drought classification method was verified by comparing the Palmer Drought Severity Index of the catchments with the drought classifications within each estuary. Droughts have demonstrable effects on estuary water column condition, notably decreases in turbidity, nutrient concentrations, and chlorophyll concentrations. Droughts do not appear to be important drivers of infaunal communities in estuarine regions with normally high salinities (25-32) although they coincide with increased diversity and changes in community composition in estuarine regions that have lower salinities (10)(11)(12)(13)(14)(15)(16)(17)(18)(19). Droughts cause decreases in Litopenaeus setiferus (white shrimp) and Callinectes sapidis (blue crab) abundances and spatial extents. This indicates that droughts, especially when combined with water diversions, may negatively affect primary and secondary productions in other semi-arid estuaries of the world.

Drought impacts on water quality and potential implications for agricultural production in the Maipo River Basin, Central Chile

“…The responses related to DO are variable but with lower significant relationships than the other parameters. We would expect decreased DO values under low flows due to a lower oxygen saturation concentration under higher water temperatures (summer droughts), higher rates of organic matter decomposition by microorganisms, and lower re-aeration rates (Prathumratana et al 2008, Van Vliet and Zwolsman 2008, Palmer and Montagna 2015. However, this positive correlation was only observed at two stations located in irrigation districts.…”

“…Although drought impacts on water quantity are well known (Van Vliet and Zwolsman 2008, Safavi and Malek Ahmadi 2015 and references therein), the consequences on water quality are not fully recognized yet (Zwolsman and van Bokhoven 2007). The low flows and water levels during hydrological droughts can affect water quality of freshwater systems by, for instance, increasing its residence time, reducing the flushing rate of water bodies with limited dilution of point source emissions and the interruption of sediment, organic matter and nutrient transport (Van Vliet and Zwolsman 2008, Mishra and Singh 2010, Mosley 2015, Palmer and Montagna 2015. Water quality characteristics such as the increase in total dissolved solids, and their constituent ions and the decrease of dissolved oxygen, could cause agronomic problems to irrigated agriculture (Sagasta andBurke 2005, Maestre-Valero andMartínez-Alvarez 2010).…”

Egg boon fatty acids reveal effects of a climatic event on a marine food web

“…Freshwater inflow is known to be very important for healthy estuarine communities. Crustaceans and the species that prey upon them are especially impacted by droughts (Palmer and Montagna ). It is, therefore, not surprising that the diet of red drum would change during the most severe drought recorded to date in the western Gulf of Mexico, but the details that were revealed by the fatty acid composition of their eggs is new and unexpected.…”

Egg Boon Fatty Acids Reveal Effects of a Climatic Event on a Marine Food Web

“…Freshwater inflow is known to be very important for healthy estuarine communities. Crustaceans and the species that prey upon them are especially impacted by droughts (Palmer and Montagna 2015). It is, therefore, not surprising that the diet of red drum would change during the most severe drought recorded to date in the western Gulf of Mexico, but the details that were revealed by the fatty acid composition of their eggs is new and unexpected.…”