| The interaction between submerged aquatic vegetation (SAV), turbidity, and water movement is modeled as a feedback in which SAV reduces water flow, thus decreasing turbidity, and promoting growth. This positive feedback can promote ecosystem shifts to an alternative state (e.g. from a high turbidity-low SAV state to low turbidity-high SAV) from which it is unlikely to revert to its previous state (hysteresis). These shifts are usually modeled for SAV and turbidity in shallow lakes. Estuaries have different controls on turbidity that complicate this model, such as high mineral contribution to turbidity, as well as high hydrologic and environmental variability. The objective of this research was to detect feedbacks between SAV and turbidity in an anthropogenically modified estuary given the multiple external controls on turbidity and the variability of the system, and to determine if these feedbacks promote hysteresis.Remote sensing was necessary to determine SAV distribution. Using a machine learning classifier, SAV was mapped in the Sacramento San Joaquin River Delta from airborne imaging spectroscopy acquired during June-July 2004-2008. Agreement between the map classes and ground reference data was "very good", although discrimination between water and SAV was difficult when SAV was sparse or deep.SAV areal cover was analyzed around in situ turbidity and velocity stations. Annual maximum water velocities from 2004-2006 that exceeded 0.49 m&dots-1 controlled SAV cover. SAV cover limits high growing season turbidities from 2004-2008: SAV has vithe most significant impact on turbidities ranging from 13.8-15.8 NTU, and this constraint on summertime turbidity is likely reducing habitat quality and quantity for the endemic and endangered fish the Delta smelt (Hypomesus transpacificus).An analysis of historic turbidity data from the same stations showed a significant decline from 1975-2008 (-1.3% of the mean site turbidity/year) the turbidity decline is highly correlated with SAV cover (R2=0.9). The relative contribution of SAV to the decreasing turbidity trend averages between 21-70% of the total trend this contribution varied with percent SAV cover. Anthropogenic activities in the watershed reduced the sediment supply into the Delta, which favored the expansion of SAV. Turbidity declines were further promoted by expanding SAV. |
