Do sediments of ephemeral and perennial streams show different impacts on water quality when subjected to the same drying conditions?

Abstract

Empirical evidence was studied to investigate whether ephemeral stream sediments have redeeming biological and physical attributes with respect to water quality, via a laboratory mesocosm study simulating stagnant pooled conditions in ephemeral and perennial streams. In addition to stream type, the effect of sediment quantity variation (sediment to water ratio) was also studied. From the water quality parameters tested (electrical conductivity, dissolved oxygen, pH, nitrogen species and phosphate), only electrical conductivity showed a significant difference between the two stream types irrespective of sediment to water ratio. However, the temporal water quality of a given stream type changed with sediment quantity in the mesocosm. Re-flooding of mesocosms after complete drying did not result in blackwater conditions, but a similar spike in nutrient concentration was observed in both stream types. The absence of blackwater was attributed to the lack of addition of new organic matter and litter, as well as the saturation of dissolved oxygen in mesocosms, therefore, indicating that aeration and litter control could be used as mitigation methods for blackwater events. It was evident that water quality variations in ephemeral streams are purely based on the flow regime (hydrological flow conditions) and organic loading. No evidence was found for any unique biological and physical properties of ephemeral sediment that redeem water quality.