Global sensitivity analysis of an end-to-end marine ecosystem model of the North Sea : factors affecting the biomass of fish and benthos

Comprehensive analysis of parameter and driver sensitivity is key to establishing the credibility of models of complex systems. This is especially so for models of natural systems where experimental manipulation of the real-world to provide controlled validation data is not possible. Models of marine ecosystems fall into this category, but despite the interest in these models for evaluating the effects of climate change and fishing on nutrient fluxes and the abundances of flora and fauna, none have yet been subjected to global sensitivity analysis. Here we present results of both local ‘one-at-a-time’ (OAT), and variance based global sensitivity analyses (GSA) of the fish and fishery aspects of StrathE2E, an end-to-end (nutrients to birds and mammals) ecosystem model of the North Sea. The sensitivity of the model was examined with respect to internal biological parameters, and external drivers related to climate and human activity. The OAT Morris method was first used to screen for factors most influential on model outputs. The Sobol GSA method was then used to calculate quantitative sensitivity indices. The results indicated that the fish and shellfish components of the model (demersal and pelagic fish, filter/deposit and scavenge/carnivore feeding benthos) were influenced by different sets of factors. Harvesting rates were directly influential on demersal and pelagic fish biomasses. Suspension/deposit feeding benthos were directly sensitive to changes in temperature, while the temperature acted indirectly on pelagic fish through the connectivity between model components of the food web. Biomass conversion efficiency was the most important factor for scavenge/carnivorous feeding benthos. The results indicate the primacy of fishing as the most important process affecting total fish biomass, together with varying responses to environmental factors which may be relevant in the context of climate change. The non-linear responses and parameter interactions identified by the analysis also highlight the necessity to use global rather than local methods for the sensitivity analysis of ecosystem models

Mechanistic origins of variability in phytoplankton dynamics. Part II: analysis of mesocosm blooms under climate change scenarios

Driving factors of phytoplankton spring blooms have been discussed since long, but rarely analyzed quantitatively. Here, we use a mechanistic size-based ecosystem model to reconstruct observations made during the Kiel mesocosm experiments (2005–2006). The model accurately hindcasts highly variable bloom developments including community shifts in cell size. Under low light, phytoplankton dynamics was mostly controlled by selective mesozooplankton grazing. Selective grazing also explains initial dominance of large diatoms under high light conditions. All blooms were mainly terminated by aggregation and sedimentation. Allometries in nutrient uptake capabilities led to a delayed, post-bloom dominance of small species. In general, biomass and trait dynamics revealed many mutual dependencies, while growth factors decoupled from the respective selective forces. A size shift induced by one factor often changed the growth dependency on other factors. Within climate change scenarios, these indirect effects produced large sensitivities of ecosystem fluxes to the size distribution of winter phytoplankton. These sensitivities exceeded those found for changes in vertical mixing, whereas temperature changes only had minimal impacts

Chemical and Toxicological Analyses of Lake Calumet (Cook County, Illinois) Sediments

HWRIC Project 88-048NTIS PB90-16072

Quantifying early risks of species invasions: factors regulating south to north bivalve colonization of novel habitats

Management of species invasions ideally requires early detection of species at low abundance, which is often challenging for traditional methods. Environmental DNA (eDNA) provides a promising tool with enhanced sensitivity relative to traditional methods. As an emerging method, however, detection of species at low abundance based on eDNA needs to be optimized to improve detection rate and reduce false negatives. I conducted a meta-analysis, the results of which suggested the significance of using the highly sensitive PCR method and extensive sampling (i.e., replicates sampling and large water volume) to improve detection rate in eDNA-based, low-abundance species detection programs. Needs for improved assay sensitivity screening, testing and reporting were also identified to reduce false negatives and to inform future uses. I developed and optimized an eDNA-based early detection method for the invasive bivalve Limnoperna fortunei (golden mussel) and applied it to investigate the spatial-temporal distribution of golden mussel DNA in the central route of South to North Water Diversion Project (SNWDP) in China. I found that improved detection could be achieved by optimizing sensitivity of the method used either through screening primer pairs or PCR methods. A primer pair with a lower limit of detection (LoD) achieved earlier and lower abundance detection of the target species relative to those with higher LoD. Water samples containing re-suspended matter from the bottom layer were better for detection than those exclusively collected from the surface layer, and only sampling the latter caused false negatives. Quantitative PCR yielded higher detection rates than conventional PCR, while the quantification efficiency was reduced in field water samples as compared to total genomic DNA. Replicate sampling was critical to reduce false negative detections. The majority of positive detections of golden mussel DNA in the main canal of SNWDP were concentrated in warm months, and the occurrence of positive detections was significantly related to minimum daily air temperature, consistent with the expected spawning season of the species. Golden mussel DNA was detected as far as ~1150 km from the putative source of the individuals, indicating long-distance transport of veligers during spawning season. Finally, I tested the functional response and size-selective clearance of the golden mussel to project their potential impacts. Results indicated that golden mussels have a type I functional response, with clearance rate inversely related to food concentration. Presence of golden mussels suppressed suspended matter concentration, the extent of which was dependent on animal abundance, particle size, and their interactions. Golden mussels packaged fine suspended particles into coarser ones, and capture efficiency was inversely related to particle size. Given the suitable habitat and continuous water flow in the main canal of the SNWDP, it seems inevitable that it will be colonized by golden mussels. Abundance mitigation should be considered for the main canal, while containment and dispersal limitation should be prioritized to prevent further spread and reduce overall impact

Driver-pressure-impact and response-recovery chains in European rivers: observed and predicted effects on BQEs

The report presented in the following is part of the outcome of WISER’s river Workpackage WP5.1 and as such part of the module on aquatic ecosystem management and restoration. The ultimate goal of WP5.1 is to provide guidance on best practice restoration and management to the practitioners in River Basin Management. Therefore, a series of analyses was undertaken, each of which used a part of the WP5.1 database in order to track two major pathways of biological response: 1) the response of riverine biota to environmental pressures (degradation) and 2) the response of biota to the reduction of these impacts (restoration). This report attempts to provide empirical evidence on the environment-biota relationships for both pathways

Environmental DNA : from detection of priority invasive species to monitoring entire macroinvertebrate communities in freshwater ecosystems

Freshwater ecosystems are among the most threatened habitats on Earth, facing challenges from a range of anthropogenic pressures. Accurate biodiversity assessment is essential to identify these pressures prior to irreversible damage. Current monitoring techniques for freshwater systems rely heavily on capture methods to infer the status of an ecosystem. However, these methods are often inefficient at detecting and identifying all species at a site and often miss those in low abundance. Emerging molecular methods such as environmental DNA (eDNA) could be a “game changer” for freshwater biodiversity monitoring. This thesis focuses on the application of eDNA for detection of invasive non-native species (INNS) and whole macroinvertebrate community assessment. Firstly, targeted eDNA PCR assays were developed for four priority freshwater INNS, and validated in mesocosm experiments and field trials. Targeted (PCR and qPCR) and passive (metabarcoding) eDNA approaches were then compared to traditional methods for detecting quagga mussels, Dreissena rostriformis bugensis. The targeted approaches were the most sensitive for detection of quagga mussels at low densities and both qPCR and metabarcoding showed correlations with mussel density. The power and utility of eDNA metabarcoding for detecting rare or unexpected taxa was then demonstrated by passive detection of a new INNS, Gammarus fossarum, in UK rivers. Finally, metabarcoding of both bulk DNA and eDNA from water and sediment was compared to the traditional method of macroinvertebrate sampling, to evaluate the potential of emerging molecular methods for ecological assessment. The results show metabarcoding approaches are not suitable to retrofit or replace existing methods of assessment, but provide an exciting opportunity for greater taxonomic identification and have the ability to detect a combination of taxa across groups, some of which are not utilised in current ecological assessment methods. This work has demonstrated a huge potential for eDNA methods to be applied to INNS monitoring and further our ability to carry out complete biodiversity assessment of waterbodies