A cost-precision model for marine environmental monitoring,based on time-integrated averages

Ongoing marine monitoring programs are seldom designed to detect changes in the environment between different years, mainly due to the high number of samples required for a sufficient statistical precision. We here show that pooling over time (time integration) of seasonal measurements provides an efficient method of reducing variability, thereby improving the precision and power in detecting inter-annual differences. Such data from weekly environmental sensor profiles at 21 stations in the northern Bothnian Sea was used in a cost-precision spatio-temporal allocation model. Time-integrated averages for six different variables over 6 months from a rather heterogeneous area showed low variability between stations (coefficient of variation, CV, range of 0.6–12.4%) compared to variability between stations in a single day (CV range 2.4–88.6%), or variability over time for a single station (CV range 0.4–110.7%). Reduced sampling frequency from weekly to approximately monthly sampling did not change the results markedly, whereas lower frequency differed more from results with weekly sampling. With monthly sampling, high precision and power of estimates could therefore be achieved with a low number of stations. With input of cost factors like ship time, labor, and analyses, the model can predict the cost for a given required precision in the time-integrated average of each variable by optimizing sampling allocation. A following power analysis can provide information on minimum sample size to detect differences between years with a required power. Alternatively, the model can predict the precision of annual means for the included variables when the program has a pre-defined budget. Use of time-integrated results from sampling stations with different areal coverage and environmental heterogeneity can thus be an efficient strategy to detect environmental differences between single years, as well as a long-term temporal trend. Use of the presented allocation model will then help to minimize the cost and effort of a monitoring program.     

A Comparison of Three Methods to Collect Submerged Aquatic Vegetation in a Shallow Lake

Two boat-based and one in-water sampling method have been used to collect submerged aquatic vegetation (SAV) as part of a long-term monitoring program in Lake Okeechobee, Florida, USA. The boat-based methods consisted of collecting SAV with a ponar dredge, used only to collect Chara, and an oyster tongs-like rake apparatus, used to collect all SAV. The in-water method involved use of a 0.5 m² PVC quadrat frame deployed by a diver. During summer 2002, SAV biomass samples were collected using all three methods at various sites in the lake to compare between-methods sampling precision. Sites used for these comparisons were selected based on plant type, plant density and sediment type. Statistical comparisons indicated that there were significant (p ≤ 0.05) biomass differences in 8 of 15 possible pairwise comparisons between sampling method biomass means. In four of the eight comparisons, significantly higher biomass mean values were obtained using the quadrat frame. In three of the remaining four comparisons, significantly higher biomass mean values were obtained with the rake apparatus. For the fourth comparison, a significantly higher biomass mean value was obtained with the ponar dredge. Three of the four relationships between SAV biomass collected by the rake and the quadrat and the rake and the quadrat/ponar dredge were statistically significant, linear and explained between 67 and 78% of the biomass variability. There were no significant differences between regression coefficients or elevations for these relationships, therefore these regressions estimated the same population regression. The population regression coefficient was 0.95, suggesting that the quadrat and ponar over-sampled relative to the rake, but the amount of this over-sampling was very small. Since there was no consistent pattern in the sampling method which yielded the significantly different biomass values and there were no significant differences in sampling precision across a range of plant species, plant densities and two sediment types, the boat-based rake method appears to be a suitable replacement for the previously used ponar dredge and quadrat methods, when in-lake measurements are not practical.     

Application of statistical modeling to optimize a coastal water quality monitoring program

The long-term water quality monitoring program implemented by the Massachusetts Water Resources Authority in 1992 is extensive and has provide substantial understanding of the seasonality of the waters in both Boston Harbor and Massachusetts Bay and the response to improvements in effluent quality and offshore transfer of the effluent in September 2000. The monitoring program was designed with limited knowledge of spatial and temporal variability and long-term trends within the system. This led to an extensive spatial and temporal sampling program. The data through 2003 showed high correlation within physical parameters measured (e.g., salinity, dissolved oxygen) and in biological measures such as chlorophyll fluorescence. To address the potential sampling redundancies in the measurement program, an assessment of the impact of reduced levels of monitoring on the ability to make water quality decisions was completed. The optimization was conducted by applying statistical models that took into account whether there was evidence of a seasonal pattern in the data. The optimization used model survey average readings to identify temporal fixed effects, model survey-average-corrected individual station readings to identify spatial fixed effects, corrected the individual station readings for temporal and spatial fixed effects and derived a correlation model for the corrected data, and applied the correlation model to characterize the correlation of annual average readings from reduced monitoring programs with true parameter levels. Reductions in the number of sampling stations were found less detrimental to the quality of the data for annual decision-making than reductions in the number of surveys per year, although there is less of a difference in this regard for dissolved oxygen than there is for chlorophyll. The analysis led to recommendations for a substantially lower monitoring effort with minimal loss of information. The recommendation supported an annual budget savings of approximately $183,000. Most of the savings was from fewer surveys as approximately $21,000 came from the reduction in the number of stations monitored from 21 to 7 and associated laboratory analytical costs.     

Inter-annual and spatial variability in hillslope runoff and mercury flux during spring snowmelt

Spring snowmelt is an important period of mercury (Hg) export from watersheds. Limited research has investigated the potential effects of climate variability on hydrologic and Hg fluxes during spring snowmelt. The purpose of this research was to assess the potential impacts of inter-annual climate variability on Hg mobility in forested uplands, as well as spatial variability in hillslope hydrology and Hg fluxes. We compared hydrological flows, Hg and solute mobility from three adjacent hillslopes in the S7 watershed of the Marcell Experimental Forest, Minnesota during two very different spring snowmelt periods: one following a winter (2009-2010) with severely diminished snow accumulation (snow water equivalent (SWE) = 48 mm) with an early melt, and a second (2010-2011) with significantly greater winter snow accumulation (SWE = 98 mm) with average to late melt timing. Observed inter-annual differences in total Hg (THg) and dissolved organic carbon (DOC) yields were predominantly flow-driven, as the proportion by which solute yields increased was the same as the increase in runoff. Accounting for inter-annual differences in flow, there was no significant difference in THg and DOC export between the two snowmelt periods. The spring 2010 snowmelt highlighted the important contribution of melting soil frost in the timing of a considerable portion of THg exported from the hillslope, accounting for nearly 30% of the THg mobilized. Differences in slope morphology and soil depths to the confining till layer were important in controlling the large observed spatial variability in hydrological flowpaths, transmissivity feedback responses, and Hg flux trends across the adjacent hillslopes.     

Effect of diel period and season on seining effort required to detect changes in Lake Erie beach fish assemblages

Using beach seining data from Lake Erie beaches, we examined the effect of diel period and season on two common study objectives considered sensitive to sampling effort: (1) has fish assemblage composition changed between two sampling time periods?, and (2) how many samples are necessary to provide a representative sample of the fish assemblage? Across a range of effect sizes and power levels, sample sizes were estimated for species richness, total fish abundance, round goby (Neogobius melanostomus) abundance and emerald shiner (Notropis atherinoides) abundance. For most sampling periods and effect sizes, several hundred to several thousand seine hauls were estimated to be required for detecting large-scale (e.g. basin-wide) changes in round goby and emerald shiner abundance. Depending on the indicator of interest, night seining (either spring or fall) was interpreted as the most efficient approach. For both seasons, sampling effort beyond 40 to 50 night seine hauls results in few additional species being detected. Both species accumulation curves and estimated sample sizes indicate that less effort is required to detect species richness changes than fish abundance. For most effect sizes and power levels, estimates of the number of seine hauls required to detect changes in fish abundance are unrealistically large for most monitoring programs. More practical monitoring strategies could be achieved by adopting alternative indicators (e.g. guilds), a more liberal significance level (p=0.1), a paired-site sampling design, or including reference sites.     

Evaluating long-term trends in littoral benthic macroinvertebrate communities of lakes recovering from acid deposition

The Mann–Kendall test has been proposed as a nonparametric method to evaluate trends in long-term water quality datasets with missing values, serial correlation, and non-normality. However, this test has rarely been used to evaluate long-term trends in biological data. In this study, we used the Mann–Kendall test to evaluate trends in 15?years of data on benthic macroinvertebrate communities from 17 Precambrian Shield lakes. We also used the van Belle and Hughes test of trend homogeneity to assess whether common among-lake temporal trends existed. We assumed that evidence of a common regional trend among lakes would support the hypothesis of long-term biological recovery from past acidification. We found decreasing proportions of Chironomidae and increasing proportions of Ephemeroptera, Plecoptera, and Trichoptera (EPT) in both single-lake and multi-lake trend analysis. Moreover, six of the nine lakes with significant trends in more than one benthos metric displayed a significant decrease in Chironomidae and increase in EPT concurrently, indicating a shift towards more acid-sensitive taxa. Weak trends in several of the biological metrics indicated that recovery in these lakes has been impeded. Results of this study indicate that the Mann–Kendall and van Belle and Hughes trend tests are useful statistical tools to evaluate long-term patterns in biological data.     

The value of long-term environmental monitoring programs: an Ohio River case study

As a subset of environmental monitoring, fish sampling programs have been an important part of assessing the potential impacts of water withdrawals and effluent discharges on fish populations for many years. New environmental regulations often require that adverse environmental impacts to fish populations be minimized. Without long-term field data, population evaluations may incorrectly indicate adverse impacts where none exist or no impact where one is likely to occur. Several electric utility companies have funded the Ohio River Ecological Research Program, which has been in existence for over 40 years and consists of fish, habitat, and water quality studies at multiple power plant sites on the mainstem Ohio River. Sampling includes seasonal night-time electrofishing and daytime beach seining at three upstream and three downstream locations near each plant. The long-term nature of the program allows for the establishment of aquatic community indices to support evaluations of technology performance, the collaborative development of compliance metrics, and the assessment of fish population trends. Studies have concluded that the Ohio River fish community has improved in response to better water quality and that power plant fish entrainment and impingement and thermal discharges have had little or no measureable impact. Through collaboration and the use of long-term data, $6.3 million in monitoring costs have been saved during recent fish impingement studies. The ability to access a multiyear fish abundance database, with its associated data on age, growth, and fecundity, improves the quality of such evaluations and reduces the need for extensive field sampling at individual locations.     

Soil microbial characteristics at the monitoring plots on windthrow areas of the Tatra National Park (Slovakia): their assessment as environmental indicators

This study focused on the responses of soil microorganisms to different management regimes on disturbed windthrow areas. Microbial parameters potentially serving as indicators of environmental changes within a long-term monitoring of forest development after large-scale disturbance events were assessed. Basal and substrate-induced respiration, N mineralisation, catalase activity, microbial biomass as well as functional diversity based on Biolog assay were determined in soil samples from three disturbed plots and an undisturbed reference plot in the Tatra National Park (Slovakia) since 2006. A relative congruence of inter-annual trends of microbial activity indicators at all plots results from a common response of microbiota to changes of climate at the landscape level after forest stands were destroyed. While catalase activity and functional diversity proved to be useful indicators of temporal trends, microbial biomass seems to reflect different management regimes at the disturbed plots.     

Design to monitor trend in abundance and presence of American beaver (Castor canadensis) at the national forest scale

Wildlife conservationists design monitoring programs to assess population dynamics, project future population states, and evaluate the impacts of management actions on populations. Because agency mandates and conservation laws call for monitoring data to elicit management responses, it is imperative to design programs that match the administrative scale for which management decisions are made. We describe a program to monitor population trends in American beaver (Castor canadensis) on the US Department of Agriculture, Black Hills National Forest (BHNF) in southwestern South Dakota and northeastern Wyoming, USA. Beaver have been designated as a management indicator species on the BHNF because of their association with riparian and aquatic habitats and its status as a keystone species. We designed our program to monitor the density of beaver food caches (abundance) within sampling units with beaver and the proportion of sampling units with beavers present at the scale of a national forest. We designated watersheds as sampling units in a stratified random sampling design that we developed based on habitat modeling results. Habitat modeling indicated that the most suitable beaver habitat was near perennial water, near aspen (Populus tremuloides) and willow (Salix spp.), and in low gradient streams at lower elevations. Results from the initial monitoring period in October 2007 allowed us to assess costs and logistical considerations, validate our habitat model, and conduct power analyses to assess whether our sampling design could detect the level of declines in beaver stated in the monitoring objectives. Beaver food caches were located in 20 of 52 sampled watersheds. Monitoring 20 to 25 watersheds with beaver should provide sufficient power to detect 15–40% declines in the beaver food cache index as well as a twofold decline in the odds of beaver being present in watersheds. Indices of abundance, such as the beaver food cache index, provide a practical measure of population status to conduct long-term monitoring across broad landscapes such as national forests.     

近十年水磨河水质变化特征研究

利用水磨河2001—2010年各断面实测资料,采用单因子法和综合污染指数法分析了近十年该流域各断面主要污染物超标情况,沿程变化特征及年际、季节变化趋势。结果表明,搪瓷厂泉断面、七纺桥断面水质有所好转,下游联丰桥断面、米泉桥断面污染程度逐渐加重,超标污染项目逐年增加。高锰酸盐指数、氨氮、总磷浓度值在联丰桥断面直线上升,石...     

Inter- and Intra-Annual Chemical Variability During the ice-Free Season in Lakes with Different Flushing Rates and Acid Deposition Histories

Quantifying chemical variability in different lake types is important for the assessment of both chemical and biological responses to environmental change. For monitoring programs that emphasize a large number of lakes at the expense of frequent samples, high variability may influence how representative single samples are of the average conditions of individual lakes. Intensive temporal data from long-term research sites provide a unique opportunity to assess chemical variability in lakes with different characteristics. We compared the intra- and inter-annual variability of four acidification related variables (Gran alkalinity, pH, sulphate concentration, and total base cation concentration) in four lakes with different flushing rates and acid deposition histories. Variability was highest in lakes with high flushing rates and was not influenced by historic acid deposition in our study lakes. This has implications for the amount of effort required in monitoring programs. Lakes with high flushing rates will require more frequent sampling intervals than lakes with low flushing rates. Consideration of specific lake types should be included in the design of monitoring programs.     

A Bayesian approach for incorporating uncertainty and data worth in environmental projects

A data worth model is presented for the analysis of alternative sampling schemes in a special project where decisions have to be made under uncertainty. This model is part of a comprehensive risk analysis algorthm with the acronym BUDA. The statistical framework in BUDA is Bayesian in nature and incorporates both parameter uncertainty and natural variability. In BUDA a project iterates among the analyst, the decision maker, and the field work. As part of the analysis, a data worth model calculates the value of a data campaign before the actual field work, thereby allowing the identification of an optimum data collection scheme. A goal function which depicts the objectives of a project is used to discriminate among different alternatives. A Latin hypercube sampling scheme is used to propagate parameter uncertainties to the goal function. In our example the uncertain parameters are the parameters which describe the geostatistical properties of saturated hydraulic conductivity in a Molasse environment. Our results indicated that failing to account for parameter uncertainty produces unrealistically optimistic results, while ignoring the spatial structure can lead to an inefficient use of the existing data.     

Biomass and number of fish impinged at a nuclear power plant by the Baltic Sea

The main aim of this study was to investigate the number and biomass of impinged fish at Forsmark Nuclear Power Plant in Sweden, located on the coast of the Baltic Sea. Of particular interest was the number of impinged individuals of the critically endangered European eel (Anguilla anguilla) which is regularly caught in the cooling system. Another aim was to determine the comparability of the results from Forsmark and results from impingement studies in other types of waters. Cross-systems studies make it possible to (1) estimate fish loss at plants where fish is not counted, and (2) to predict changes in fish loss from changes in electricity production or cooling water use. In 2010, 31,300,000 fish with a total biomass of 62,600 kg were impinged at Forsmark. In 2011, 27,300,000 fish weighing 38,500 kg were impinged. The maximum peak in total fish number and biomass occurred in spring. The most critical period for herring was in late summer and early autumn. Regarding eel, the largest impingement losses were recorded in November. The number of fish agreed with earlier established quantities of impinged fish in both freshwater and marine ecosystems. The study also estimated that 1,300 critically endangered eels could survive at Forsmark each year if a fish return system would be constructed to allow the passage of fish from the plant back to the Baltic Sea.     

Network design factors for assessing temporal variability in ground-water quality

Benchmark major ions and nutrients data were collected biweekly for about two years at 12 wells at two sites in a shallow sand and gravel aquifer in west-central Illinois. The purpose of the study was to explore the time series properties of ground-water quality data collected at a relatively high sampling frequency. A secondary purpose was to determine the relative magnitudes of natural and sampling-related sources of variance in ground-water quality time series. The absence of this kind of information has severely hindered the design of ground-water sampling programs in the past.An autocorrelation analysis showed that the median sampling frequency for which the predicted ratio of effective independent sample size to total sample size was 0.5 (50% sampling redundancy) ranged from 6 to 14 samples per year. For a predicted ratio of effective independent sample size to total sample size of 0.9 (10% sampling redundancy) the sampling frequency ranged from 3 to 6 samples per year. This suggests that, for the wells sampled, sampling frequencies much higher than monthly can result in considerable loss of information, and may not be cost effective. Care was taken in the design of the field and laboratory sampling protocol to minimize the effects of measurement error. The data analysis confirmed that this goal was accomplished. In most cases considerably less than five percent of the total variability could be attributed to sampling and analytical error. Because of the relatively short duration of the study (42 biweekly sampling occasions at most wells) it was not possible to identify the magnitude of seasonal variations reliably.     

Impacts of climate warming on vegetation in Qaidam Area from 1990 to 2003

The observed warming trend in the Qaidam area, an arid basin surrounded by high mountains, has caused land surface dynamics that are detectable using remotely sensed data. In this paper, we detected land-cover changes in the Qaidam Area between 1990 and 2003 in attempt to depict its spatial variability. The land-cover changes were categorized into two trends: degradation and amelioration, and their spatial patterns were examined. Then we estimated the correlation coefficients between growing-season NDVI and several climatic factors with the consideration of duration and lagging effects. The results show that the inter-annual NDVI variations are positively correlated with May to July precipitations, but not significantly correlated with sunshine duration. We observed no obvious trend in precipitation or sunshine duration from 1990 to 2003. Thus, the authors suggest that their slight fluctuations may not be responsible to the decade-scaled land-cover changes. However, our results indicate a good positive relationship between the NDVI trend and climate warming in the ameliorated areas, but a negative one in the degraded areas. By statistical analyses, we found that degradations mainly occurred at the oasis boundaries and at lower elevations in the non-oasis regions where effective soil moisture might have been reduced by the warming-caused increase in evapotranspiration. At higher elevations where thermal condition acts as a major limiting factor, ameliorations were unequivocally detected, which is attributable to the direct facilitation by temperature increases. We suggest that the impacts of the observed climate warming on vegetation are spatially heterogeneous, depending on the combinations of thermal condition and moisture availability.     

The effect of visitors’ pressure on the spatial variability of sandy soil in an urban parks in Tel Aviv

The effect of visitors' pressure on the spatial variability of soil properties was investigated in three open green areas in Tel Aviv. Six types of micro-environments were chosen: under oak and pine tree canopy with low (OL and PL) and high (OH and PH) visitors' pressure; herbaceous area without visitors' pressure (HE); and resting area under high visitors' pressure (RA). For each micro-environment soil samples were collected from the upper 0-5 cm depth for organic matter content and moisture determination. Before sampling, soil surface compaction and litter biomass were measured. Soil properties were affected by visitors' pressure and by the type of micro-environment. Soil organic matter content and soil moisture proved significantly higher under oak trees at low visitors' pressure. Average litter biomass significantly decreased with increasing visitors' pressure in the tree micro-environments. Average penetration depth decreased significantly with increased visitors' pressure in all micro-environments. In all the cases where averages significantly decreased, variance significantly decreased too, but the coefficient of variations increased. This means that variances changed slower than averages. Changes in averages were accompanied by a change of data population structure, which indicated more soil spatial homogeneity under high visitors' pressure. The data from different intervals of data population of soil properties demonstrated the different sensitivity to visitors' pressure.     

Biomonitoring of polychlorinated biphenyls (PCBs) in heavily polluted aquatic environment in different fish species

The distribution and concentrations of polychlorinated biphenyls (PCBs) were determined in fish species (European perch Perca fluviatilis, northern pike Esox lucius, pike perch Sander lucioperca, wels catfish Silirus glanus, common carp Cyprinus carpio, European eel Anguilla anguilla, freshwater bream Abramis brama, goldfish Carassius auratus, and roach Rutilus rutilus) in a heavily polluted water reservoir Zemplínska ?írava (Slovakia). The study performed at two different time points 5?years apart (2004 and 2009) revealed serious PCB contamination of fish muscle tissue and significant interspecies as well as tissue-specific differences in PCB uptake by fish. Total PCBs broadly correlated with the trophic position of individual fish species within a food chain (P??0.05). The study has shown that the kind of fish, its feeding habit, and specific conditions of the habitat are mutually interrelated factors that are responsible for significant variations in fish body burdens. A tendency to PCB biomagnification was also proved in some fish species of this water reservoir.     

Seasonal and Inter-Annual Variations in Methyl Mercury Concentrations in Zooplankton from Boreal Lakes Impacted by Deforestation or Natural Forest Fires

We compared the effects of natural and anthropogenic watershed disturbances on methyl mercury (MeHg) concentration in bulk zooplankton from boreal Shield lakes. MeHg in zooplankton was monitored for three years in nine lakes impacted by deforestation, in nine lakes impacted by wildfire, and in twenty lakes with undisturbed catchments. Lakes were sampled during spring, mid- and late summer. MeHg in zooplankton showed a seasonal trend: concentrations were the lowest in spring, then peaked in mid-summer and decreased in late summer. Over the three study years, MeHg concentrations observed in mid-summer in zooplankton from forest harvested lakes were significantly higher than in reference and fire-impacted lakes, whereas differences between these two groups of lakes were not significant. The pattern of distribution of MeHg in zooplankton during the different seasons paralleled that of dissolved organic carbon (DOC), which is known as a vector of Hg from watershed soils to lake water. Besides DOC, MeHg in zooplankton also showed a positive significant correlation with epilimnetic temperature and sulfate concentrations. An inter-annual decreasing trend in MeHg was observed in zooplankton from reference and fire-impacted lakes. In forest harvested lakes, however, MeHg concentrations remained higher and nearly constant over three years following the impact. Overall these results indicate that the MeHg pulse observed in zooplankton following deforestation by harvesting is relatively long-lived, and may have repercussions to the accumulation of MeHg along the food chain. Therefore, potential effects of deforestation on the Hg contamination of fish should be taken into account in forest management practices.     

Statistical modeling of crystalline silica exposure by trade in the construction industry using a database compiled from the literature

A quantitative determinants-of-exposure analysis of respirable crystalline silica (RCS) levels in the construction industry was performed using a database compiled from an extensive literature review. Statistical models were developed to predict work-shift exposure levels by trade. Monte Carlo simulation was used to recreate exposures derived from summarized measurements which were combined with single measurements for analysis. Modeling was performed using Tobit models within a multimodel inference framework, with year, sampling duration, type of environment, project purpose, project type, sampling strategy and use of exposure controls as potential predictors. 1346 RCS measurements were included in the analysis, of which 318 were non-detects and 228 were simulated from summary statistics. The model containing all the variables explained 22% of total variability. Apart from trade, sampling duration, year and strategy were the most influential predictors of RCS levels. The use of exposure controls was associated with an average decrease of 19% in exposure levels compared to none, and increased concentrations were found for industrial, demolition and renovation projects. Predicted geometric means for year 1999 were the highest for drilling rig operators (0.238 mg m(-3)) and tunnel construction workers (0.224 mg m(-3)), while the estimated exceedance fraction of the ACGIH TLV by trade ranged from 47% to 91%. The predicted geometric means in this study indicated important overexposure compared to the TLV. However, the low proportion of variability explained by the models suggests that the construction trade is only a moderate predictor of work-shift exposure levels. The impact of the different tasks performed during a work shift should also be assessed to provide better management and control of RCS exposure levels on construction sites.