Characterizing estuarine salinity patterns with event duration and frequency of reoccurrence approaches

Abstract

Salinity is widely recognized as a dominant environmental variable in estuarine systems. However, drawing clear causal relationships between salinity and estuarine floral or faunal patterns of abundance, population status, or vigor is often confounded by the great spatial and temporal variation exhibited by salinity. Averages, or other statistics, over monthly, seasonal, or longer periods are often used, but may fail to capture patterns of ecological significance. This study introduces a novel approach to characterize estuarine salinity based on deriving events of specific magnitude and duration from a long-term record; events that are also amenable to analysis of the frequency that they reoccur. With sufficient point data for salinity over the spatial domain of an estuary, these variables can be mapped and contoured to reveal spatial patterns of potential ecological significance. Model-predicted salinity for a large estuary system of the Texas coast was used to develop and test these new techniques. While this system has great variation in salinity, both temporally and spatially, we find that this variability can be characterized into well-defined and reoccurring salinity-based events. Furthermore, the frequency of reoccurrence of those events over a long-term record reveals patterns not captured by more common techniques such as averaging over similar time frames. These novel techniques provide an integrated spatial-temporal approach to salinity pattern portrayal which may be useful for examining short-term (daily-monthly) estuary processes and longer-term (yearly-decadal) limits to estuary species distributions and habitat composition.