Resilience in Coastal Weltand Systems – Why it matters and how it can be determined

Freshwater, marine, and terrestrial ecosystems are experiencing significant changes as a result of human activity and anthropogenic climate change. The ability of ecosystems to tolerate changes in state variables and processes while continuing to maintain core ecological functions in the wake of disturbances is defined as resilience. Tipping points are observed in systems with strong positive feedback, providing early warning signals of potential instability. These points can be detected through metrics associated to a theoretical notion described as critical slowing down (CSD), such as increased recovery time, variance, and autocorrelation. Here we present CSD analysis of the Coastwide Reference Monitoring System (CRMS) dataset which covers the extent of the Mississippi Delta and coastal area in Louisiana, USA. CRMS consists of a defined sampling schedule and standardised data collecting methods across 390 sites. The CRMS stations span the whole coast of Louisiana, situated across nine coastal basins. Four transects were selected, of which fifteen stations across 3 Transects along the coastline and another six stations located closer to the Mississippi river, located further inland. Using a set of quantitative, analytical methods based on the assessment of changes in variance and autocorrelation we determine the current state and likelihood to be at CSD, so to demonstrate how to operationalise what to date has been developed as a theoretical framework. We use wavelets as a measure of identifying changes in the variance term, and autocorrelation was modelled using a Bayesian dynamic linear model. We are able to describe the long term ecological impact of climate high energy disturbance events such as intense tropical storms or low energy events such as extensive droughts through the analysis of the spatio-temporal patterns in the long term water quality monitoring stations.