Modeling the Impacts of Multiple Environmental Stress Factors on Estuarine Copepod Populations

Many studies have focused on natural stress factors that shape the spatial and temporal distribution of calanoid copepods, but bioassays have shown that copepods are also sensitive to a broad range of contaminants. Although both anthropogenic and natural stress factors are obviously at play in natural copepod communities, most studies consider only one or the other. In the present investigation, we modeled the combined impact of both anthropogenic and natural stress factors on copepod populations. The model was applied to estimate <i>Eurytemora affinis</i> densities in the contaminated Scheldt estuary and the relatively uncontaminated Darß-Zingst estuary in relation to temperature, salinity, chlorophyll <i>a</i>, and sediment concentrations of cadmium, copper, and zinc. The results indicated that temperature was largely responsible for seasonal fluctuations of <i>E. affinis</i> densities. Our model results further suggested that exposure to zinc and copper was largely responsible for the reduced population densities in the contaminated estuary. The model provides a consistent framework for integrating and quantifying the impacts of multiple anthropogenic and natural stress factors on copepod populations. It facilitates the extrapolation of laboratory experiments to ecologically relevant end points pertaining to population viability

Sediment and metal deposition.

<p>Box plots (median, 25^th, 75^th percentile and standard deviation) of seasonal difference in deposited sediments (A) and deposited Cd (B) in a tidal marsh and restored marsh (CRT).</p

Correlation coefficients (R-values) between the different metals and sediment characteristics.

<p>All correlations were significant (p<0.001).</p

Average metal concentrations (µg g⁻¹), calculated metal deposition per surface unit (µg cm⁻² y⁻¹) and estimated total accumulated metals in the different zones of the Schelde estuary (10³ kg y⁻¹).

<p>The average estimated sedimentation rate (kg m⁻² y⁻¹) and total surface for the marshes (in 2012) and expected future areas displayed.</p

Modeled Cd deposition in a developping marsh.

<p>Modeled evolution of marsh elevation and Cd deposition. Elevation of the marsh and mean high water level (MHWL), both in m TAW (Belgian reference height) on the left Y-axis. Cd deposition (µg cm⁻² a⁻¹) on the right Y-axis.</p

Detailed map of the study area.

<p>Sampling locations for the subtidal samples, tidal flat and tidal marsh samples along a transect and the location of the CRT.</p

Average metal concentrations (µg g⁻¹) and sediment characteristics (% dw) in the different areas for winter and summer.

<p>Significant differences (p<0.05) between seasons within an area are underlined and differences between areas within a season are indicated with letters (a, b, c for winter; x, y, z for summer).</p

Estimated input and output of trace metals in the Schelde estuary (10³ kg y⁻¹), based on literature and own calculations (^aBaeyens et al. (1997) [6]; ^bDe Smedt et al. (1997) [8]; ^cBaeyens et al. (2005) [38]; ^dThis study).

<p>Total metal deposition (tons per year) and metal removal in marshes of the entire estuary compared the estimated riverine input (%), for the period 2005–2010 and for a future scenario with an additional surface area of restored marshes implemented.</p

Map of the area.

<p>Location of the Schelde estuary (A) and the study area (CRT) within the estuary (B).</p