Browsing by Author "Shilla, Daniel A."

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    The effects of catchment land use on water quality and macroinvertebrate assemblages in Otara Creek, New Zealand
    (2011-03) Shilla, Dativa J.; Shilla, Daniel A.
    The effect of catchment land use on water quality and macroinvertebrate communities was examined by using data gathered during a 2004 reconnaissance of nine sites in the Otara Creek, New Zealand. Data collected included macroinvertebrate, water chemistry and sediments characteristics. Macroinvertebrate data were used in metric and index calculations. A total of 61 macroinvertebrate taxa, with 3032 total individuals, were identified from the macroinvertebrates samples collected from nine sites in Otara Creek. The greatest number of macroinvertebrate taxa was recorded within bush sites (mean>25), while the urban sites had the least number of taxa (mean=10). Pasture sites were intermediate with the mean>17. Taxa number differed significantly across land use. Mean macroinvertebrates abundance varied across the sites and land uses. The highest macroinvertebrates mean abundance was recorded in urban and pasture sites, while bush sites had significantly lower mean abundance. Physico-chemical parameters decreased from bush toward urban streams. Biotic indices were sensitive to changes in macroinvertebrates community structure across land uses with mean scores decreasing from bush to urban and pasture streams. Ordination of biological data showed a clear separation of bush from urban and pastures streams. Analysis of similarities revealed significant differences in macroinvertebrates between both stream groups and land-use groups. The observed macroinvertebrate assemblage pattern was best correlated with a single variable, conductivity, temperature, turbidity, nitrate and dissolved oxygen. The combination of these environmental variables best explained the changes in the macroinvertebrate assemblages between sites. This study demonstrates that catchment land use may significantly affect the water quality and macroinvertebrate communities in an ecosystem.
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    Effects of Riparian Vegetation and Bottom Substrate on Macroinvertebrate Communities at Selected Sites in the Otara Creek, New Zealand
    (2012-07) Shilla, Dativa J.; Shilla, Daniel A.
    The effects of riparian vegetation and bottom substrate on water quality and macroinvertebrate communities were assessed by utilising data gathered during a 2004 reconnaissance of nine sites in the Otara Creek, New Zealand. The aim of the study was to use multivariate statistical techniques to better explain the specific environmental factors that drive biological communities in an environment. During the survey, macroinvertebrate assemblages were sampled along with water quality, bottom substrate, riparian vegetation and habitat assessments. Multivariate statistical analyses of habitat and channel characteristics, physical conditions and water quality data were used to determine the relationship between environmental variables and the macroinvertebrate community structure. Ordination of biological and environmental data showed a clear separation of bush from urban and pastures streams. The observed macroinvertebrates assemblage pattern was best correlated with a single variable, riparian width (r = 0.81), a combination of two variables: cobbles and riparian width (r = 0.88), three variables: boulders, nitrate and riparian width (r = 0.91) and five variables: habitat score, shade, boulders, nitrate and riparian width (r = 0.94). The BIO-ENV procedure showed that habitat and channel characteristics had the greatest relationship to macroinvertebrate community structure followed by water chemistry.
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    Terrigenous nutrient and organic matter in a subtropical river estuary, Okinawa, Japan: origin, distribution and pattern across the estuarine salinity gradient
    (2011-06) Shillaa, Dativa J.; Tsuchiya, Makoto; Shilla, Daniel A.
    Estuaries and their associated rivers are organically rich sites that play an important role in the removal and transformation of organic matter and nutrients derived from terrigenous and anthropogenic sources. This study conducted comprehensive field surveys from March 2010 to January 2011 to study the downstream pattern and distribution of nutrients (NO , NO, NH and PO) and dissolved organic carbon (DOC) and particulate organic carbon (POC) and nitrogen (PN) in the surface waters of the Manko estuary, a subtropical estuary in Okinawa, Japan. Fatty acid (FA) analysis and POC–C/N ratios were used to further identify variations in the sources of particulate organic matter along the estuary during summer (July) and winter (January). The results suggest that the estuary contains high concentrations of dissolved inorganic (N and P) and organic (DOC) nutrients, which are largely influenced by terrestrial sources from the Kokuba and Noha rivers, and moderate levels of particulate nitrogen and carbon. In general, suspended particles and dissolved nutrients followed sedimentation and biotic uptake patterns common in other subtropical estuaries. Thus, an important fraction of terrestrial materials was rapidly sinking along the estuary and was replaced with estuarine and marine-derived materials at mid- to high-salinity along the estuary. The FA signatures suggested that bacteria, domestic and agricultural waste-derived organic matter were the dominant sources of suspended organic matter in the Manko estuary. Overall, despite the relatively high terrestrial and anthropogenic influences in the Manko estuary, effective processing of different sources and forms of terrigenous organic matter in the estuarine salinity gradient significantly reduces their signatures prior to export to the coastal ocean.