Remarkably little is known about the effectiveness or rates of recovery of aquatic ecosystems from reductions in human-associated pressures at landscape scales. The retention of anthropogenic contaminants within ecosystems can retard rates of recovery considerably, while the trajectories of recovery processes vary with the extent of disturbance and the resilience of biotic assemblages. The Great Irish Famine of 1845-1850 comprised one of the most significant human disasters of the 19th century, causing the death of approximately one million people and the emigration of a further two million from the country between 1845 and 1855. We found, through analysis of detailed historical census data combined with paleolimnological investigation of sedimentary nutrient concentrations, stable isotope ratios, and diatom assemblages, that the trophic level of Lough Carra, a largely shallow calcareous lake in the west of Ireland with no urban areas or point sources of any significance in its catchment, reduced considerably during and immediately after the Great Famine, shifting to new equilibria within just 2-10 years. Our results demonstrate that the reduction of human pressures from diffuse sources at landscape scales can result in the rapid and monotonic recovery of aquatic ecosystems. Moreover, the recovery of ecosystems from diffuse pollution need not necessarily take longer than recovery from pollution from point sources.

We developed a mass balance ecosystem network model for Georges Bank, a highly productive and intensively studied marine system located off the New England coast. This effort is part of a broader initiative, the Energy Modeling and Analysis eXercise (EMAX), to describe ecosystem characteristics of major ecoregions of the Northeast Continental Shelf of the United States. Energy budgets for this system developed over the last six decades have progressively increased in complexity. Our analysis is based on a 33 compartment model, ranging from phytoplankton to marine mammals, seabirds, and humans for the period 1996-2000. Levels of primary production on the Bank are high relative to many other continental shelf ecosystems. Analysis of mixed trophic impacts indicates the pervasive influence of primary producers throughout the system, indicative of a system subject to important bottom-up forcing. We demonstrate the importance of the microbial food web in energy flow in the system, indicated by high levels of throughput for this component. Our analysis differs from previous energy budgets for Georges Bank in providing substantially higher estimates of zooplankton production, producing a different perspective on what had been perceived as a lower than expected ratio of secondary to primary production that was attributed to export processes. Relative species composition of the fish community differed markedly in our analysis relative to previous energy budgets for this system, with a dominance by small pelagic fishes. Despite these differences, the estimated biomass levels were roughly comparable to those from prior studies. Estimates of system developmental capacity and overhead suggest a highly resilient system.

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