Stressor-response Models Research Articles

Improving multiple stressor-response models through the inclusion of nonlinearity and interactions among stressor gradients.

Stressor-response models are used to detect and predict changes within ecosystems in response to anthropogenic and naturally occurring stressors. While nonlinear stressor-response relationships and interactions between stressors are common in nature, predictive models often do not account for them due to perceived difficulties in the interpretation of results. We used Irish river monitoring data from 177 river sites to investigate if multiple stressor-response models can be improved by accounting for nonlinearity, interactions in stressor-response relationships and environmental context dependencies. Out of the six models of distinct biological responses, five models benefited from the inclusion of nonlinearity while all six benefited from the inclusion of interactions. The addition of nonlinearity means that we can better see the exponential increase in Trophic Diatom Index (TDI3) as phosphorus increases, inferring ecological conditions deteriorating at a faster rate with increasing phosphorus. Furthermore, our results show that the relationship between stressor and response has the potential to be dependent on other variables, as seen in the interaction of elevation with both siltation and nutrients in relation to Ephemeroptera, Plecoptera and Trichoptera (EPT) richness. Both relationships weakened at higher elevations, perhaps demonstrating that there is a decreased capacity for resilience to stressors at lower elevations due to greater cumulative effects. Understanding interactions such as this is vital to managing ecosystems. Our findings provide empirical support for the need to further develop and employ more complex modelling techniques in environmental assessment and management.

Establishing biologically relevant sediment organic matter thresholds for estuaries and embayments of the Southern California Bight, USA

• Thresholds for sediment TOC and TN were predictive of healthy, intact macrobenthic communities. • Decline in macrobenthos condition with increasing gradients of sediment organic matter. • Thresholds were consistent with other coastal ocean sites in Northern Hemisphere. • First study to put forth sediment TN thresholds protective of benthic community condition. • Thresholds could be used as a guideline in the management of eutrophication stressors. Estuaries, lagoons, and embayments are key components of the coastal ecosystem and they are pervasively exposed to a variety of stressors – the most common of which is eutrophication. In shallow water coastal systems, eutrophication typically manifests as shifts in sediment oxygen horizons and accumulation of toxic reduced compounds in the porewater, which have direct, negative effects on the benthic fauna that live in these sediments. To catalog, prevent, and remediate these stressors, the coastal zone management community has expressed a need to identify targets for biostimulatory compounds and products in the environment that are protective of biological integrity of coastal waters. In response to this need, the present study identified and validated a series of sediment total organic carbon (TOC) and total nitrogen (TN) concentrations associated with changes in macrobenthic community composition across the estuaries and embayments of the Southern California Bight (SCB). Using data from a regional monitoring program, benthic community condition, quantified using the M-AMBI condition assessment index, was modelled as a function of TOC or TN concentration using logistic regression. Then, we evaluated eutrophication thresholds at concentrations corresponding to several relative probabilities (from 0.6 to 0.8), reflecting a range of policy makers’ potential tolerance for risk of failing to meet biointegrity goals. Organic matter thresholds were extracted from the regressions that were predictive of healthy macrobenthic community condition at a 0.8 probability (1.23 mg g −1 TN, 15.51 mg g −1 TOC), 0.7 probability (2.58 mg g -1 TN, 22.9 mg g −1 TOC), or 0.6 probability (3.68 mg g −1 TN, 28.96 mg g −1 TOC) – as an illustration of how these types of stressor response models could be used to set targets for management of these ecosystems. These thresholds were subsequently validated by applying them to data held back from the model creation and by comparing them to taxon-specific inflection points identified from TITAN changepoint analysis of the macrobenthic/TOC/TN calibration data. The different TOC and TN thresholds correctly classified between 67 and 86% of the validation samples, with most of the misclassifications being instances of low organic matter concentration but poor community condition (i.e., false positives). The TOC thresholds identified from our Southern California dataset fell within a similar range (10–35 mg g −1 ) that has been linked to benthic community impacts from a variety of coastal ocean sites across the Northern Hemisphere. The consistency in thresholds across multiple habitats and different types of biota is suggestive of a general, quantitative threshold for organic matter accumulation in near shore sediment habitats and could be useful for informing the management of coastal ecosystems and setting targets biostimulatory stressors in these systems.

Impacts of climate change and land use on the development of nutrient criteria

Numeric criteria are crucial for controlling cultural eutrophication and for protecting current and future water quality. Anthropogenic climate change and the modification of land use have the potential to influence the development of nutrient criteria. In this study, stressor-response models, land use-nutrient regression models, and terrestrial ecosystem health states were used to determine the criterion values of total nitrogen (TN), total phosphorous (TP), and chlorophyll a (Chl a) using field data from lakes and reservoirs in Heilongjiang Province. Analysis of covariance and nonlinear regressions were used to quantitatively characterize the impact of climate change on the development of nutrient criteria. The results indicated that there were no significant differences in the nutrient criteria obtained by the various methods. Climate change factors (such as temperature, precipitation, and wind speed) are predicted to influence the relationships between nutrients and Chl a, as well as land use and nutrient concentrations, as climate change persists. Climate change should be considered during the development of nutrient criteria, as climate-driven change and achieving a desired water quality without the threat of eutrophication in the future will require stricter nutrient criteria than those needed under the current climate conditions.

Modeled hydrologic metrics show links between hydrology and the functional composition of stream assemblages.

Flow alteration is widespread in streams, but current understanding of the effects of differences in flow characteristics on stream biological communities is incomplete. We tested hypotheses about the effect of variation in hydrology on stream communities by using generalized additive models to relate watershed information to the values of different flow metrics at gauged sites. Flow models accounted for 54-80% of the spatial variation in flow metric values among gauged sites. We then used these models to predict flow metrics in 842 ungauged stream sites in the mid-Atlantic United States that were sampled for fish, macroinvertebrates, and environmental covariates. Fish and macroinvertebrate assemblages were characterized in terms of a suite of metrics that quantified aspects of community composition, diversity, and functional traits that were expected to be associated with differences in flow characteristics. We related modeled flow metrics to biological metrics in a series of stressor-response models. Our analyses identified both drying and base flow instability as explaining 30-50% of the observed variability in fish and invertebrate community composition. Variations in community composition were related to variations in the prevalence of dispersal traits in invertebrates and trophic guilds in fish. The results demonstrate that we can use statistical models to predict hydrologic conditions at bioassessment sites, which, in turn, we can use to estimate relationships between flow conditions and biological characteristics. This analysis provides an approach to quantify the effects of spatial variation in flow metrics using readily available biomonitoring data.

Estimating nutrient criteria of the lakes and reservoirs by reference condition approach and stressor-response models

Estimating nutrient criteria of the lakes and reservoirs by reference condition approach and stressor-response models

Non-chemical Risk Assessment for Lifting and Low Back Pain Based on Bayesian Threshold Models

BackgroundSelf-reported low back pain (LBP) has been evaluated in relation to material handling lifting tasks, but little research has focused on relating quantifiable stressors to LBP at the individual level. The National Institute for Occupational Safety and Health (NIOSH) Composite Lifting Index (CLI) has been used to quantify stressors for lifting tasks. A chemical exposure can be readily used as an exposure metric or stressor for chemical risk assessment (RA). Defining and quantifying lifting nonchemical stressors and related adverse responses is more difficult. Stressor–response models appropriate for CLI and LBP associations do not easily fit in common chemical RA modeling techniques (e.g., Benchmark Dose methods), so different approaches were tried.MethodsThis work used prospective data from 138 manufacturing workers to consider the linkage of the occupational stressor of material lifting to LBP. The final model used a Bayesian random threshold approach to estimate the probability of an increase in LBP as a threshold step function.ResultsUsing maximal and mean CLI values, a significant increase in the probability of LBP for values above 1.5 was found.ConclusionA risk of LBP associated with CLI values > 1.5 existed in this worker population. The relevance for other populations requires further study.

Using algal biomass to evaluate numeric nutrient criteria in an estuary: A case study of Daliaohe Estuary in China

This paper presents an initial inquiry into model-based numeric nitrogen and phosphorus criteria for estuaries based on stressor-response models between nutrients and algal biomass (Chl-a concentration) and further studies the effect of salinity (S) on nutrient criteria. Field data collection and associated indoor modeling were conducted in Daliaohe Estuary. Dissolved inorganic nitrogen (DIN), total nitrogen (TN), phosphate (PO43−) and total phosphorus (TP) eco-criteria of Daliaohe Estuary in China were calculated at salinities of 15, 25 and 31. The results suggested that the variation in S had significant influence on the DIN and TN eco-criteria and no obvious effect on the PO43− and TP eco-criteria. The values of DIN and TN eco-criteria increased with either higher or lower salinity concentrations, and were strongly linked to the effects of salinity on algal nutrient absorption and utilization, growth, metabolism, and osmotic pressure.

Diatom taxa and assemblages for establishing nutrient criteria of lakes with anthropogenic hydrologic alteration

Stressor-response models offer guidance for concentration-based nutrient criteria in lakes under human intervention. Diatom-based statistics from biological responses were incorporated to derive taxon-specific and community-level change points (thresholds) of phosphorous and nitrogen in 77 Yangtze floodplain lakes. Diatom metrics relating with conductivity were adopted as response variables, since conductivity explained the maximum variation (38.1%) in diatom assemblages via Bootstrapped regression trees. Nonparametric change-point analysis and Threshold Indicator Taxa ANalysis showed threshold responses of diatom community structure at 0.05–0.08mgTP/L in connected lakes and 0.02–0.04mgTP/L in isolated lakes. Distinct community change points of sensitive diatoms occurred at 0.96–1.63mgTN/L in connected lakes and 0.52–0.63mgTN/L in isolated lakes. Diatom community structures of tolerant taxa were substantially altered beyond 0.22–0.23mg/L in connected lakes and 0.52–0.69mgNOx/L in isolated lakes. Hydrological river-lake connectivity differed significantly in ecological nutrient criteria with more TN/TP criteria and less NOx criteria in connected lakes. Given the ecological significance and biological integrity, diatom-based statistics can provide more reliable change points (thresholds) for nutrient criteria than Chl a-nutrient relationships.

Bedded Sediment Conditions and Macroinvertebrate Responses in New Mexico Streams: A First Step in Establishing Sediment Criteria

AbstractExcess fine sediments in streambeds are among the most pervasive causes of degradation in streams of the United States. Simple criteria for acceptable streambed fines are elusive because streambed fines and biotic tolerances vary widely in the absence of human disturbances. In response to the need for sediment benchmarks that are protective of minimum aquatic life uses under the Clean Water Act, we undertook a case study using surveys of sediment, physical habitat, and macroinvertebrates from New Mexico streams. Our approach uses weight of evidence to develop suggested benchmarks for protective levels of surficial bedded sediments <0.06 mm (silt and finer) and <2.0 mm (sand and finer). We grouped streams into three ecoregions that were expected to produce similar naturally occurring streambed textures and patterns of response to human disturbances. Within ecoregions, we employed stressor response models to estimate fine sediment percentages and bed stability that are tolerated by resident macroinvertebrates. We then compared individual stream sediment data with distributions among least‐disturbed reference sites to determine deviation from natural conditions, accounting for natural variability across ecoregion, gradient, and drainage area. This approach for developing benchmark values could be applied more widely to provide a solid basis for developing bedded sediment criteria and other protective management strategies in other regions.

Using Stressor–Response Models to Derive Numeric Nutrient Criteria for Lakes in the Eastern Plain Ecoregion, China

AbstractLakes in the Eastern Plain ecoregion of China are typically shallow, experience large disturbances, and are hydrologically connected to rivers. In recent years, lake eutrophication in this ecoregion has intensified due to human activities. To determine important regional nutrient criteria, the effects of hydrologic features and disturbances should be taken into account. In this paper, annual average data were used to construct stressor–response models for each hydrological lake type identified for lakes in the Eastern Plain ecoregion. In these models, total nitrogen (TN) and total phosphorus (TP) criteria were obtained from a chlorophyll a (Chl‐a, response variable) threshold value. A Chl‐a concentration of 4.73 μg L−1 was identified as this threshold value, which was based on the cyanotoxin limits associated with drinking water supply. The three lake types, which differed in hydrological structure, had significantly different TN and TP criteria. For example, lakes connected to the Yangtze River (T1) had a TN criterion ranging from 0.594 to 0.838 mg L−1, which was substantially higher than those for lakes that were never connected to the river (T3, 0.234–0.422 mg L−1). The exception to this trend occurred for lakes that were historically but not currently connected to the river (T2) due to P‐limitation in this lake type. However, there was little variability in the TP criterion among T1, T2, and T3 lakes, the values of which ranged from 0.021 to 0.037, 0.023 to 0.042, and 0.028 to 0.041 mg L−1, respectively.

Determining ecoregional numeric nutrient criteria by stressor-response models in Yungui ecoregion lakes, China

The importance of developing numeric nutrient criteria has been recognized to protect the designated uses of water bodies from nutrient enrichment that is associated with broadly occurring levels of nitrogen/phosphorus pollution. The identification and estimation of stressor-response models in aquatic ecosystems has been shown to be useful in the determination of nutrient criteria. In this study, three methods based on stressor-response relationships were applied to determine nutrient criteria for Yungui ecoregion lakes with respect to total phosphorus (TP), total nitrogen (TN), and planktonic chlorophyll a (Chl a). Simple linear regression (SLR) models were established to provide an estimate of the relationship between a response variable and a stressor. Multiple linear regressions were used to simultaneously estimate the effect of TP and TN on Chl a. A morphoedaphic index (MEI) was applied to derive nutrient criteria using data from Yungui ecoregion lakes, which were considered as areas with less anthropogenic influences. Nutrient criteria, as determined by these three methods, showed broad agreement for all parameters. The ranges of numeric nutrient criteria for Yungui ecoregion lakes were determined as follows: TP 0.008-0.010 mg/L and TN 0.140-0.178 mg/L. The stressor-response analysis described will be of benefit to support countries in their numeric criteria development programs and to further the goal of reducing nitrogen/phosphorus pollution in China.

Stressor–Response Models: A Practical Application for the Development of Lake Nutrient Criteria in China

Stressor–Response Models: A Practical Application for the Development of Lake Nutrient Criteria in China