Charles K. Minns

Forecasting impacts of climate change on Great Lakes surface water temperatures

ABSTRACT Temperature influences the rates of many ecosystem processes. A number of recent studies have found evidence of systematic increases in Great Lakes surface water temperatures. Our study aims to construct empirical relationships between surface water temperatures and local air temperatures that can be used to estimate future water temperatures using future air temperatures generated by global climate models. Remotely sensed data were used to model lake-wide average surface water temperature patterns during the open-water period in Lakes Superior, Huron, Erie, and Ontario. Surface water temperatures typically exhibit linear warming through the spring, form a plateau in mid-summer and then exhibit linear cooling in fall. Lake-specific warming and cooling rates vary little from year to year while plateau values vary substantially across years. These findings were used to construct a set of lake-specific empirical models linking surface water temperatures to local air temperatures for the period 1995–2006. Hindcasted whole-lake water temperatures from these models compare favourably to independently collected offshore water temperatures for the period 1968–2002. Relationships linking offshore water temperatures to inshore water temperatures at specific sites are also described. Predictions of future climates generated by the Canadian Global Climate Model Version 2 (CGCM2) under two future greenhouse gas emission scenarios are used to scope future Great Lakes surface water temperatures: substantial increases are expected, along with increases in the duration of summer stratification.

Factors Affecting Fish Species Richness in Ontario Lakes

Abstract A large data set on Ontario lakes and their fish species was examined for evidence of the influence on species richness of regional, local, anthropogenic, and methodological factors. Analysis of regional species distributions and associations showed patterns consistent with species invasion into Ontario since the last period of glaciation. A comparison of local species richness (mean richness among lakes) with regional richness pointed to a dominance of local over regional factors in determining lake species richness. A multiple regression model of species richness accounted for 48% of variance. Of the two regional factors included in the model, watershed species richness increased lake species richness and elevation decreased it. An increase in two local abiotic factors, lake area and mean depth, increased richness. Richness also increased with increasing pH, an anthropogenic factor, and increased in more recent survey years, an indicator of methodological effects. Analyses of mean species richn...

The potential future impact of climate warming and other human activities on the productive capacity of Canada's lake fisheries: a meta-model

A simple meta-model was used to examine how climate warming and stresses due to other human activities might affect the productive capacity of fisheries in all of Canadas lakes. Recent estimates of lake resource characteristics by secondary watershed and area size-class provided the basis for the model. Potential fishery productivity was estimated using a variant of the Schlesinger and Regier (1982) model which had lake mean depth, total dissolved solids concentration, and mean annual air temperature as inputs. A business-as-usual climate change scenario (SRES A2) was used to estimate worst case future temperature increases (4.5–8.3°C by the 2080s). The stress index from Chu et al. (2003) was used as a proxy for the impact on fisheries of other human activities. Projected populations for the SRES A2 scenario were used to scale future stress index levels. Potential biotic responses to warming were represented in two ways; the first as potential biotic displacement of currently dominant species when temperature rose beyond their preferred range and the second as potential biotic adaptation of other species, particularly in species rich areas, replacing displaced species. Potential productive capacity of fisheries in all Canadian lakes was 361,000 tonnes for the baseline climate norms period of 1961–1990. Climate warming increased productivity by 80.7% in the 2080s but stress reduced levels by 19.4% in the norms period and held the increase to 10.3% in the 2080s. Biotic displacement alone resulted in large decreases in productivity, by 65.2% in the 2080s and, when stress was added, by 79.5%. Biotic adaptation largely offset displacement. Applying stress and both biotic responses productivity was reduced by 31.4% in the 2080s from the unstressed norms baseline or 12% with stress added. Further investigations are needed to better establish the likely extent of stress impacts and potential biotic responses to climate warming in Canadas lakes.

Submerged aquatic vegetation in the Bay of Quinte: Response to decreased phosphorous loading and Zebra Mussel invasion

Originally mesotrophic, the Bay of Quinte ecosystem has experienced eutrophication since the 1940s, which resulted in the decline of once-lush submerged aquatic vegetation (SAV) beds in the upper bay by the mid-1960s. Since 1972, twelve SAV surveys have been conducted along ten index transects, recording:% cover, distance SAV beds extended from shore (extent), maximum depth of colonization (Zc), species composition, and, in later years, wet plant biomass. Offshore secchi depth and ϵpar, (the vertical light extinction rate (m−1) for photosynthetically active radiation), were also recorded either weekly or bi-weekly during the growing season since 1972. During this time, two major changes occurred within the bay: the reduction in point-source phosphorus (P-control) loadings in 1978 and the 1993 invasion by Dreissenid Mussel. SAV response to these changes varied temporally and spatially, with the shallow upper bay showing the greatest response, particularly after Zebra Mussels establishment. In the upper bay, mean secchi depth increased by 8% from 1.2 m prior to P-control (pre-P), to 1.3 m after P-control (post-P) and further increased by 46% to 1.9 m after Dreissena establishment (post-D). Upper bay SAV responded to these invasive species with increases in the means of three variables: Zc from 1.6 to 3.5 m, extent from 114 m to 417 m and wet biomass from 50 g m−2 to 962 g m−2. SAV in the middle and lower bays were in better condition in 1972, with pre-P cover in excess of 50% and Zc of 2.6 and 3.7 m, respectively. SAV cover did increase in the post-D (1994 to 2007) period by approximately 25% and Zc increased to 3.7 and 6.5 m, but the narrow fringing strip of shallower water along the shore in these two deeper bays limited substantial increases in bed extent. Both water clarity and basin morphometry strongly influenced SAV distribution and abundance within the Bay of Quinte.

A Computer Model of Biomass Dynamics and Food Competition with Implications for its Use in Fishery Management

Abstract A model useful for managing interacting fish species, based on concepts of food competition, is developed and tested. The model consists of differential equations. One, in the Pearl-Verhulst idiom, specifies organisms which can serve only as food resources for consumers of higher trophic status. A storage equation describes ingestion and assimilation of food by a consumer. Another equation derived with the storage equation describes growth and attrition (i.e., metabolic and mortality costs) in terms of energy. Further, consumers may prey upon each other in addition to the resources and the equations are shown to be adequate for describing food webs. The model is essentially one of energy flow and deals with biomass, instead of numerical, dynamics. Coded in a computer language (PL/I), the model simulates competition and clarifies aspects of yield and harvest strategies in systems of interacting populations. The model is illustrated with hypothetical populations which have variable turnover rates...

Management of Great Lakes fisheries: Progressions and lessons

Fishery resources include the fishes, the other biota they interact with, and the habitats they occupy. The historical sequences in the use and management of these resources may be considered as a series of interacting sequences of change. These sequences can span from social, economic, institutional and landscape changes, through water quality, habitat supply, and climate changes, to biotic composition changes, introductions and extinctions, and species harvest changes. A selection of these sequences is examined for the St. Lawrence-Great Lakes which has been subjected to intense development and study over the last 200 years. While the whole basin is considered, some detailed attention is given to Lake Ontario and, within it, the Bay of Quinte. Brief selective development histories are given for the three areas as context. The management history is outlined and critiqued. While much progress has been achieved in cleaning up the load-driven problems in the basin, little secure progress toward rehabilitation and sustainability has been achieved. In the current period of economic problems, governments, particularly Canadas, are undoing past ecosystem management progress. The development of St. Lawrence-Great Lakes ecosystem science has drawn heavily from both oceanography and limnology. A brief, selective overview of several progressions in ecosystem science illustrates how knowledge and understanding of this ecosystem has expanded over the last 60 years, providing an improved basis for management action. As with use and management, the science of fishery resource management has consisted of many historical progressions. The many sequences in the St. Lawrence-Great Lakes management and science histories lend support for recognition of (i) the importance of taking an ecosystem approach to renewable resource management, (ii) the value of adaptive management practices and, particularly, (iii) the vital complementary roles of long-term monitoring and mathematical modelling.

The science of ecosystem-based management on a global scale: The Laurentian Great Lakes, Lake Ontario, and the Bay of Quinte as a nested case study

Lake ecosystems are our sentinels of environmental change and their effective management is one of our key planetary challenges in the 21st century. The evolution of ecosystem science as a basis for management is reviewed using the nested set of the Laurentian Great Lakes, Lake Ontario, and the Bay of Quinte as a primary focus. Other great lakes of the world, many of which are in Canada, provide a secondary focus. Ecosystem science has a long history in the Laurentian Great Lakes with developments driven in large part by the Great Lakes Water Quality Agreement, Lake-Wide Management Plans, and Remedial Action Plans for Areas of Concern. By comparison most other large Canadian lakes have received little attention as is the case with many of the worlds great lakes. The substantial arsenal of tools and knowledge accumulated in the Great Lakes can serve as a model for other lake systems. As the range of ecosystem management problems has continued to grow, the motivating theme has shifted from restoration through rehabilitation to adaptation. The main challenge is to coalesce the many stresses we previously have sought to manage singly: land use, population growth, habitat degradation, resource exploitation, invasive species, pollutant and contaminant loadings, and, finally, climate change. Essential features of effective ecosystem-based management are: a whole system view, active adaptive management, acceptance of science-based evidence, and shared goals with common objectives. The last two may prove the greatest hurdle as society becomes ever more divided and fractious given the global onslaught of environmental and societal challenges. The Great Lakes experience shows there is hope.

Uncertainty assessment of trophic flows in Hamilton Harbour: A linear inverse modelling analysis

Ecopath with Ecosim has been extensively used to examine ecosystem attributes and the effects of management actions. One of the main limitations in using Ecopath to credibly guide management decisions lies in the quality and quantity of the data used. Linear Inverse Modelling treats the problem of ecosystem characterization in a rigorous mathematical way in which the foodweb is described as a (linear) function of the flows and model parameters are (inversely) derived from observed data. In this study, our thesis is that Linear Inverse Modelling can be used as a complement to Ecopath applications to evaluate our confidence in typically reported ecosystem characterizations. Based on a simplified version of a previously published foodweb topology (Hossain et al., 2012), we demonstrate that there is considerable uncertainty associated with the predicted energy flows within the ecosystem of Hamilton Harbour, Lake Ontario, Canada. Uncertainty related to external flows (e.g. respiratory and detrital flows) appears to be much higher than for internal flows associated with predator-prey relationships. Our Linear Inverse Modelling analysis reinforces earlier findings that most of the trophic flows are concentrated within the first two trophic levels, while mass fluxes at the higher trophic levels are significantly lower. The intermediate ecotrophic efficiency for zooplankton suggests that planktivorous fishes do not fully capitalize upon the available food in the system. Our model estimates that a substantial amount of the detrital material is being recycled by the microbial community within the system. Taken together with the significant detrital pool directly supporting zooplankton and oligochaetes/chironomids, this prediction is consistent with recent empirical evidence that particulate organic matter from various allochthonous or autochthonous origins constitute important components of the energy transferred to higher trophic levels. Overall, our Linear Inverse Modelling analysis offers meaningful insights that should contribute towards the development of a reliable ecosystem model for Hamilton Harbour.