A GIS approach to sediment displacement in mixed sand and gravel beach environments.

Mixed sand and gravel beaches pose special management issues as they are morphologically distinct from either pure sand or shingle beaches. On the mixed sand and gravel beaches of the Canterbury Bight, New Zealand, displacement of sediments operates within a two-part sediment transport system. The large sediments are retained in the beaches, while the fine sand, silt, and mud are transported offshore to the continental shelf. While the susceptibility of sediments to size-reduction is dependent on the textural mixture of sediments, the actual size-reduction takes place during sediment transport, or displacement, in the active surf zone of the beach. The authors outline a method that incorporates the sediment reduction susceptibility of beach sediments from the textural mixture, twenty years of wave-hindcast data, and sediment tracer experiments to model sediment displacement in mixed sand and gravel beach environments of the Canterbury Bight. Results show that the textural mix of the sediments influences not only the rate of loss to size-reduction but also the time taken for sediment to be transported along a beach continuum within the surf zone. The authors modelled time-frames to achieve three target percentages of sediment displacement: (1) ten percent, (2) fifty percent, and (3) a range of zero to one hundred percent. Ten percent displacement of sediments was predicted to take between four and eighty-eight weeks, fifty percent displacement between one and sixteen years, and a hundred percent displacement up to two-hundred and thirty years, depending on the textural composition of sediments along the coast based on the actual wave action occurring along this coastline.

Resting Stage of Plankton Diversity from Singapore Coastal Water: Implications for Harmful Algae Blooms and Coastal Management.

Resting strategies of planktonic organisms are important for the ecological processes of coastal waters and their impacts should be taken into consideration in management of water bodies used by multiple industries. We combined different approaches to evaluate the importance of resting stages in Singapore coastal waters. We used molecular approaches to improve the knowledge on Singapore biodiversity, we sampled and extracted cysts from sediments to evaluate the density of resting stages in Johor Strait, and we compared systematically information on Singapore planktonic biodiversity to existing published information on resting stages from these reported organisms. This is the first study evaluating the importance of resting stages in Singapore waters. Above 120 species reported in Singapore are known to produce resting stages though no previous work has ever been done to evaluate the importance of these strategies in these waters. The results from the resting stage survey confirmed 0.66 to 5.34 cyst g-1 dry weight sediment were present in the Johor Strait suggesting that cysts may be flushed by tidal currents into and out of the strait regularly. This also suggest that the blooms occurring in Singapore are likely due to secondary growth of Harmful Algae Bloom species in the water rather than from direct germination of cysts from sediment. Finally, we discuss the importance of these resting eggs for three main national industries in Singapore (shipping, marine aquaculture and provision of drinking water through seawater desalination). We argue that this study will serve as a baseline for some of the future management of Singapore waters.

Application of Polar Organic Chemical Integrative Sampler (POCIS) to monitor emerging contaminants in tropical waters.

Tools specifically validated for tropical environments are needed to accurately describe the behavior of chemical contaminants in tropical ecosystems. In the present study, sampling rates (Rs) were determined for the commercial pharmaceutical-type Polar Organic Chemical Integrative Sampler (POCIS) with a 45.8cm(2) exposure surface for 35 Pharmaceutically Active Compounds (PhACs) and Endocrine Disrupting Compounds (EDCs), of which eight compounds (albuterol, atorvastatin, diltiazem, dilantin, enalapril, norfluoxetine, risperidone and warfarin) were reported for the first time. These sampling rates were measured in an outdoor laboratory calibration setup to best capture diurnal tropical temperature variations (29±3°C). The effect of stirring and salinity was investigated. For all compounds, the sampling rates were higher under stirred conditions as compared to quiescent conditions. Calibration results in the presence of 30g sodium chloride support that the effects of salinity on POCIS sampling rates are compound-specific. Comparisons between Time-Weight Average (TWA) water concentrations using POCIS and spot sample levels in the field (2 lake and 1 mangrove estuary sites) are presented. Results showed that POCIS TWA concentrations were in agreement with spot sample concentrations for these aquatic systems. Results indicate that POCIS can be used to effectively measure the TWA concentration for a range of PhACs and EDCs in tropical waters. However, based on the results from mass balance and field deployments, POCIS did not appear suitable for compounds with a low mass balance recovery during calibration (e.g. triclosan and linuron in this study).

Habitat loss through disruption of constrained dispersal networks.

Large losses of habitat could be caused by land use change that disrupts the dispersal networks used by migratory species. We assessed the relative losses of habitat for diadromous fish (i.e., those migrating between sea and freshwater) due to physical barriers, degradation of migratory passage associated with catchment land use, and site-scale land use characteristics on the West Coast, South Island, New Zealand. Fish occurrence, land use data, and river network models were analyzed in a GIS and subjected to a three-level hierarchical analysis. To identify accessible habitat not restricted by physical barriers, we used the migratory distance and maximum downstream slope encountered to identify accessible sites in least-impacted catchments and applied the results to all catchments within the study area. For two fish species, banded kokopu (Galaxias fasciatus) and koaro (G. brevipinnis), sites modeled as accessible using logistic regression in least-impacted catchments were then used to assess the impacts of catchment-scale deforestation and downstream land uses on habitat loss. Finally, sites not restricted by physical barriers or land-use-related impacts on migratory passage were used to model the effects of local land use. The models indicated that koaro and banded kokopu potentially had access to 28,000 km and 5300 km, respectively, of the 40,600 km of streams within the study area. Impacts due to intensive agricultural land use downstream in catchments affecting migratory passage were predicted to reduce the accessible habitats for koaro and banded kokopu by 55% and 70%, respectively. Local land use further reduced koaro and banded kokopu habitats to 70% and 90%, respectively, of total accessible habitat. Habitat lost through disruption of the dispersal network was disproportionately large because potentially useable habitat was rendered inaccessible.

A GIS approach to model sediment reduction susceptibility of mixed sand and gravel beaches.

The morphological form of mixed sand and gravel beaches is distinct, and the process/response system and complex dynamics of these beaches are not well understood. Process response models developed for pure sand or gravel beaches cannot be directly applied to these beaches. The Canterbury Bight coastline is apparently abundantly supplied with sediments from large rivers and coastal alluvial cliffs, but a large part of this coastline is experiencing long-term erosion. Sediment budget models provide little evidence to suggest sediments are stored within this system. Current sediment budget models inadequately quantify and account for the processes responsible for the patterns of erosion and accretion of this coastline. We outline a new method to extrapolate from laboratory experiments to the field using a geographical information system approach to model sediment reduction susceptibility for the Canterbury Bight. Sediment samples from ten representative sites were tumbled in a concrete mixer for an equivalent distance of 40 km. From the textural mixture and weight loss over 40 km tumbling, we applied regression techniques to generate a predictive equation for Sediment Reduction Susceptibility (SRS). We used Inverse Distance Weighting (IDW) to extrapolate the results from fifty-five sites with data on textural sediment composition to field locations with no data along the Canterbury Bight, creating a continuous sediment reductions susceptibility surface. Isolines of regular SRS intervals were then derived from the continuous surface to create a contour map of sediment reductions susceptibility for the Canterbury Bight. Results highlighted the variability in SRS along this coastline.

Spatial modeling and habitat quantification for two diadromous fish in New Zealand streams: a GIS-based approach with application for conservation management.

We developed logistic regression models from data on biotic and abiotic variables for 172 sites on Banks Peninsula, New Zealand, to predict the probability of occurrence of two diadromous fish, banded kokopu (Galaxias fasciatus) and koaro (G. brevipinnis). Banded kokopu occurrence was positively associated with small streams and low-intensity land uses (e.g., sheep grazing or forested), whereas intensive land uses (e.g., mixed sheep and cattle farming) and lack of riparian forest cover impacted negatively on occurrence at sampled sites. Also, if forests were positioned predominantly in lowland areas, banded kokopu occurrence declined with increasing distance to stream mouth. Koaro occurrence was positively influenced by catchment forest cover, high stream altitudes, and areas of no farming activity or mixed land uses. Intensive land uses, distance to stream mouth, and presence of banded kokopu negatively influenced koaro occupancy of stream reaches. Banded kokopu and koaro presence was predicted in 86.0% and 83.7% agreement, respectively, with field observations. We used the models to quantify the amount of stream reaches that would be of good, moderate, and poor quality, based on the probability of occurrences of the fish being greater than 0.75, between 0.75 and 0.5, or less than 0.5, respectively. Hindcasting using historical data on vegetation cover undertaken for one catchment, Pigeon Bay, showed they would have occupied most of the waterway before anthropogenic modification. We also modeled potential future scenarios to project potential fish distribution.