Showing papers by "Donald A. Jackson published in 2007"

Will northern fish populations be in hot water because of climate change

Abstract: Predicted increases in water temperature in response to climate change will have large implications for aquatic ecosystems, such as altering thermal habitat and potential range expansion of fish species. Warmwater fish species, such as smallmouth bass, Micropterus dolomieu, may have access to additional favourable thermal habitat under increased surface-water temperatures, thereby shifting the northern limit of the distribution of the species further north in Canada and potentially negatively impacting native fish communities. We assembled a database of summer surface-water temperatures for over 13 000 lakes across Canada. The database consists of lakes with a variety of physical, chemical and biological properties. We used general linear models to develop a nation-wide maximum lake surface-water temperature model. The model was extended to predict surface-water temperatures suitable to smallmouth bass and under climate-change scenarios. Air temperature, latitude, longitude and sampling time were good predictors of present-day maximum surface-water temperature. We predicted lake surface-water temperatures for July 2100 using three climate-change scenarios. Water temperatures were predicted to increase by as much as 18 °C by 2100, with the greatest increase in northern Canada. Lakes with maximum surface-water temperatures suitable for smallmouth bass populations were spatially identified. Under several climate-change scenarios, we were able to identify lakes that will contain suitable thermal habitat and, therefore, are vulnerable to invasion by smallmouth bass in 2100. This included lakes in the Arctic that were predicted to have suitable thermal habitat by 2100.

Reconstructing community relationships: the impact of sampling error, ordination approach, and gradient length

Abstract: Effectively summarizing complex community relationships is an important feature in studies such as biodiversity, global change, and invasion ecology. The reliability of such community summaries depends on the degree of sampling variability that is present in the data, the structure of the data, and the choice of ordination method, but the relative importance of these factors is not understood. We compared the validity of results from different ordination methods by applying five levels of sampling error to a simulated coenoplane model at two gradient lengths using two types of data (abundance and presence-absence). The multivariate methods we compared were correspondence analysis (CA), detrended correspondence analysis (DCA), non-metric multidimensional scaling (NMDS), principal component analysis (PCA) and principal coordinates analysis (PCoA). Our results showed CA and PCA using presence-absence data were the most successful methods regardless of sampling error and gradient length, closely followed by the other methods using presence-absence data. With abundance data, PCA and CA were the most successful approaches with the short and long gradients, respectively. Approaches based on PCoA and NMDS using abundance data did not perform well regardless of the choice of distance measure used in the analysis. Both of these methods, along with the PCA using abundance data, were strongly affected by the longer gradient, leading to more distorted results.

Estimating dioxin-like polychlorinated biphenyl toxic equivalents from total polychlorinated biphenyl measurements in fish

Abstract: Polychlorinated biphenyls (PCBs) are 209 related compounds, a dozen of which are known as dioxin-like PCBs (dl-PCBs) and are among the most toxic PCBs. Polychlorinated biphenyls contribute to many adverse effects to human health, including cancer, and are a major cause of fish advisories in North America. It is a common perception that individual PCB compounds, especially dl-PCBs, rather than total PCB need to be quantified to predict the environmental hazard because of differences in their toxicity potential and distribution among various environmental matrices, including aquatic food webs. Because the current analytical methods for quantifying dl-PCBs are complex and four- to fivefold more expensive, limited fish samples are analyzed for dl-PCBs. Using what likely is the largest dl-PCB fish data set (n = 912) with a wide distribution of fish species (n = 22), size (19-112 cm), weight (100-14,300 g), sex (male:female, 51:49), and PCB contamination level (20-7,300 ng/g wet wt), we show that the comparatively less expensive and rapid measurements of total PCB in fish can be utilized to assess dl-PCB-related toxicological hazard, measured as 2,3,7,8-tetrachlorodibenzo-p-dioxin toxic equivalents (TEQ). A regression equation of dl-PCB-related TEQ (i.e., TEQdl-PCB) to total PCB in fish is presented (TEQdi-PCB = [2.56 x 10(-5)]CtotalPCB, r = 0.89, p < 0.001). The regression was evaluated by applying it to three independent data sets of substantial sizes (n = 55, 141, and 176). The TEQdl-PCB estimated using the regression and total PCB measurements were within a reasonable factor of two to three of the TEQdl-PCB calculated from the dl-PCB measurements. The successful evaluation indicates versatility of the regression.

Uncertainty analysis of dioxin-like polychlorinated biphenyls-related toxic equivalents in fish.

Abstract: The toxic equivalent (TEQ) concept is widely used to assess toxicity potential of a dioxin-like chemical mixture. The TEQ approach converts concentrations of various dioxin-like compounds into a single concentration that is toxicologically equivalent to the most toxic dioxin compound, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), using toxic equivalency factors (TEFs). It has been shown that in the absence of costly measurements of dioxin-like polychlorinated biphenyls (dl-PCBs) in fish, relatively inexpensive measurements of total PCB can be utilized to estimate dl-PCB–related TEQ (i.e., TEQdl-PCB). The present study assesses the impacts of uncertainties in dl-PCB measurements and estimates, and mammalian TEFs on TEQdl-PCB using the Monte Carlo technique. The analysis suggests that measurement errors for dl-PCBs translate into up to 1.3-fold uncertainty in TEQdl-PCB, while uncertainties in estimates of dl-PCBs generally produce up to a threefold uncertainty in TEQdl-PCB. In contrast, the uncertainty due to TEFs normally ranges 10- to 13-fold and spans over 30- to 40-fold under extreme cases. For 2005 TEFs, PCB-126 is the dominating contributor to uncertainty in TEQdl-PCB. When we considered uncertainties in the TEFs and estimated dl-PCB concentrations simultaneously, there was little increase in uncertainty in TEQdl-PCB that was already produced by the TEFs only. These results indicate that the dl-PCB composition in fish and/or the relationship between total PCB and TEQdl-PCB can be utilized to estimate TEQdl-PCB with reasonable confidence.