The impacts of climate change on estuarine ecosystems : a case study on the Eden estuary, Fife, Scotland

Abstract

The Eden Estuary is a small, coastal inlet situated in Fife between the Tay and Forth Estuaries on the east coast of Scotland. A multidisciplinary case study of the estuary was conducted over a three year period observing the dynamic responses of biotic and abiotic behaviour to long term patterns of climate variability. Historical Trend Analysis (HTA) was combined with autocorrelation and spectral density analysis to identify trends, patterns and periodicity in natural cycles. River flow and wind direction data were cross-correlated with the North Atlantic Oscillation Index (NAOI) to link local responses to patterns of northern hemisphere circulation, and with Wolfe Sunspot Numbers representing variable solar activity as a potential driving mechanism for climate driven change. Assessment of the current state of ‘estuary health’ used a proxy analysis of ecosystem function, combining Bray-Curtis similarity nMDS of macrofaunal community diversity with species functional traits. The observed estuary responses were subsequently projected onto the forecasted climate change scenarios reported by the IPCCAR4, UKCIP09 and to modelled projections of solar activity to propose future trajectories of change for the estuary. Autocorrelation analysis of river flow and wind direction data identified significant (95%) correlations corresponding to solar, lunar, planetary and volcanic events. Spectral density analysis similarly identified significant (>95%) frequencies corresponding to known periods of solar activity, lunar cycles and Bruckner climatic cycles. Formal cross -correlation revealed significant (95%) relationships between both river flow and wind data with the NAOI, and using a longer times series, between river Thames annual flow and Wolfe sunspot numbers; correlating solar maximums with high flow. Periods consistent to Schwabe and Hale solar cycles were evident in the wind and river data however the NAOI only displayed Hale periodicity, inferring the river and wind data are not solely influenced (or potentially driven) by the NAO. No detrimental impact of estuary change was observed in the biotic responses inferring maintenance of estuary health. This study identifies potential driving mechanisms of estuary perturbation and whilst causal mechanisms can only be proposed, these observations form a baseline for future targeted modelling, monitoring and management.