Impact of the spatial resolution of satellite remote sensing sensors in the quantification of total suspended sediment concentration: A case study in turbid waters of Northern Western Australia

The impact of anthropogenic activities on coastal waters is a cause of concern because such activities add to the total suspended sediment (TSS) budget of the coastal waters, which have negative impacts on the coastal ecosystem. Satellite remote sensing provides a powerful tool in monitoring TSS concentration at high spatiotemporal resolution, but coastal managers should be mindful that the satellite-derived TSS concentrations are dependent on the satellite sensor's radiometric properties, atmospheric correction approaches, the spatial resolution and the limitations of specific TSS algorithms. In this study, we investigated the impact of different spatial resolutions of satellite sensor on the quantification of TSS concentration in coastal waters of northern Western Australia. We quantified the TSS product derived from MODerate resolution Imaging Spectroradiometer (MODIS)-Aqua, Landsat-8 Operational Land Image (OLI), and WorldView-2 (WV2) at native spatial resolutions of 250 m, 30 m and 2 m respectively and coarser spatial resolution (resampled up to 5 km) to quantify the impact of spatial resolution on the derived TSS product in different turbidity conditions. The results from the study show that in the waters of high turbidity and high spatial variability, the high spatial resolution WV2 sensor reported TSS concentration as high as 160 mg L-1 while the low spatial resolution MODIS-Aqua reported a maximum TSS concentration of 23.6 mg L-1. Degrading the spatial resolution of each satellite sensor for highly spatially variable turbid waters led to variability in the TSS concentrations of 114.46%, 304.68% and 38.2% for WV2, Landsat-8 OLI and MODIS-Aqua respectively. The implications of this work are particularly relevant in the situation of compliance monitoring where operations may be required to restrict TSS concentrations to a pre-defined limit

Species traits explaining sensitivity of snakes to human land use estimated from citizen science data

Understanding how traits affect species responses to threats like habitat loss may help prevent extinctions. This may be especially true for understudied taxa for which we have little data to identify declines before it is too late to intervene. We used a metric derived from citizen science data on snake occurrences to determine which traits were most correlated with species' sensitivity to human land use. We found that snake species that feed primarily on vertebrates, that use a high proportion of aquatic habitats, and that have small geographic ranges occurred in more natural and less human-dominated landscapes. In contrast, body size, clutch (or litter) size, the degree of exposure to human-dominated landscapes, reproductive mode, habitat specialization, and whether a species was venomous or not had less effect on their sensitivity to human land use. Our results extend previous findings that higher trophic position is correlated with extinction risk in many vertebrates by showing that snake species that feed primarily on vertebrates are more sensitive to human land use – a primary driver of extinction. It is likely that conversion of natural landscapes for human land use alters biotic communities, causing losses of important trophic groups, especially in aquatic and riparian communities. Practitioners should therefore prioritize preserving aquatic habitat and natural landscapes with intact biotic communities that can support species at higher trophic levels, as well as focus monitoring on populations of range-restricted species

Sulfur cycling in the water column of Little Rock Lake, Wisconsin

The S cycle in the water column of a small, soft-water lake was studied for 9 years as part of an experimental study of the effects of acid rain on lakes. The two basins of the lake were artificially separated, and one basin was experimentally acidified with sulfuric acid while the other served as a reference or control. Spatial and seasonal patterns of sulfate uptake by plankton (53-70 mmol m-2 yr-1), deposition of sulfur to sediments in settling seston (53 mmol m-2 yr-1), and sulfate diffusion (0-39 mmol m-2yr-1) into sediments were examined. Measurements of inputs (12-108 mmol m-2 yr-1) and outputs (5.5-25 mmol m-2 yr-1) allowed construction of a mass balance that was then compared with rates of S accumulation in sediments cores (10-28 mmol m-2 yr-1) and measured fluxes of S into the sediments. Because of the low SO2-4 concentrations (μmoleL-1) in the lake, annual uptake by plankton (53-70 mmol m-2 yr-1) represented a large fraction (\u3e 50%) of the SO2-4 inventory in the lake. Despite this large flux through the plankton, only small seasonal fluctuations in SO2-4 concentrations (μmole L-1) were observed; rapid mineralization of organic matter (half-life \u3c 3 months) prevented sulfate depletion in the water column. The turnover time for sulfate in the water column is only 1.4 yr; much less than the 11-yr turnover time of a conservative ion in this seepage lake. Sulfate diffusion into and reduction in the sediments (0-160 μmole m-2d-1) caused SO2-4 depletion in the hypolimnion. Modeling of seasonal changes in lake-water SO2-4 concentrations indicated that only 30-50% of the diffusive flux of sulfate to the sediments was permanently incorporated in solid phases, and about 15% of sulfur in Settling seston was buried in the sediments. The utility of sulfur mass balances for seepage lakes would be enhanced if uncertainty about the deposition velocity for both sulfate aerosols and SO2, uncertainty in calculation of a lake-wide rate of S accumulation in sediments, and uncertainty in the measured diffusive fluxes could be further constrained