Water Use Conflict and Coordination between Agricultural and Wetlands—A Case Study of Yanqi Basin

Increased groundwater extraction leads to the decrease of the extent of wetlands due to the implementation of a water-saving transformation project in an arid irrigation area. The application of integrated mitigation tools and strategies in China have increasing significance. In this study, an integrated approach (SWAT-MODFLOW) was followed; it is based on a soil and water assessment tool (SWAT) coupled with a modular three-dimensional finite difference groundwater model (MODFLOW). Recharge and evaporation values were estimated by SWAT and were then used to simulate groundwater in a MODFLOW model. Calibration (over the years 2000–2010) and validation (over the years 2010–2016) were performed, based on observed groundwater-level data; results showed that the combined SWAT-MODFLOW provides more accurate simulation and prediction of the dynamic changes of surface water and groundwater in irrigation areas than results from individual MODFLOW models. This method was applied to the Yanqi Basin, which is one of the most appropriate arid agricultural basins for modeling lake wetland and groundwater in China. The correlation coefficients (R2) between the simulated and real groundwater level are 0.96 and 0.91 in SWAT-MODFLOW and MODFLOW, respectively. With the gradual increase in the extraction to 248%, 0.62 × 108 m3 of groundwater discharged into the lake became −2.25 × 108 m3. The lake level drops 1.3 m compared with the current year, when the groundwater exploitation increases by 10 × 108 m3/year. Overall, the results of the coupling model offer scientific evidence for agricultural water management and lake recovery, so as to enhance the water use coordination.

Rapid Recent Recovery from Acidic Deposition in Central Ontario Lakes

In many regions, chemical recovery in lakes from acidic deposition has been generally slower than expected due to a variety of factors, including continued soil acidification, climate-induced sulphate (SO4) loading to lakes and increases in organic acidity. In central Ontario, Canada, atmospheric sulphur (S) deposition decreased by approximately two-thirds between 1982 and 2015, with half of this reduction occurring between 2005 and 2015. Chemical recovery in the seven lakes was limited prior to 2005, with only small increases in pH, Gran alkalinity and charge-balance ANC (acid-neutralizing capacity). This was because lake SO4 concentrations closely followed changes in S deposition, and decreases in base cation concentration closely matched declines in SO4. However, decreases in S deposition and lake SO4 were more pronounced post-2005, and much smaller decreases in lake base cation concentrations relative to SO4 resulted in large and rapid increases in pH, alkalinity and ANC. Dissolved organic carbon concentrations in lakes increased over the study period, but had a limited effect on lake recovery. Clear chemical recovery of these lakes only occurred after 2005, coinciding with a period of dramatic declines in S deposition.

Recovery of acidified Sudbury, Ontario, Canada, lakes: a multi-decade synthesis and update

The Sudbury region of northeastern Ontario, Canada, provides one of the world’s best examples of the resilience of aquatic ecosystems after reductions in atmospheric contaminant deposition. Thousands of lakes around the Sudbury metal smelters were badly damaged by acid deposition. Lakes closest to the smelters were also contaminated by metal particulates. However, large reductions in atmospheric SO2 and metal emissions starting in the early 1970s have led to widespread chemical improvements in these lakes, and recovery has been observed for various aquatic biota. Studies of Sudbury-area lakes are advancing our understanding of chemical and biological lake recovery; however, recovery is a complicated process and much remains to be learned. Biological recovery has often been slow to follow chemical recovery, and it has become apparent that the recovery of lakes from acidification is closely linked to interactions with other large-scale environmental stressors like climate change and Ca declines. Thus, in our multiple-stressor world, recovery may not bring individual lakes back to their exact former state. However, with time, substantial natural biological recovery toward typical lake communities can be reasonably expected for most but not necessarily all biota. For organisms with limited dispersal ability, particularly fish, human assistance may be necessary to re-establish typical communities. In lakes where food webs have been severely altered, re-establishment of typical diverse fish communities may in fact be an important element aiding the recovery of other important components of aquatic ecosystems including zooplankton and benthic macroinvertebrates. In the lakes closest to the smelters, where historically watersheds as well as lakes were severely damaged, the recovery of aquatic systems will be closely linked to ongoing terrestrial recovery and rehabilitation, particularly through the benefits of increased inputs of terrestrially derived organic matter. The dramatic lake recovery observed in the Sudbury area points to a brighter future for these lakes. However, continued monitoring will be needed to determine future changes and help guide the management and protection of Sudbury-area lakes in this multiple-stressor age.

The dilemma of controlling cultural eutrophication of lakes

The management of eutrophication has been impeded by reliance on short-term experimental additions of nutrients to bottles and mesocosms. These measures of proximate nutrient limitation fail to account for the gradual changes in biogeochemical nutrient cycles and nutrient fluxes from sediments, and succession of communities that are important components of whole-ecosystem responses. Erroneous assumptions about ecosystem processes and lack of accounting for hysteresis during lake recovery have further confused management of eutrophication. I conclude that long-term, whole-ecosystem experiments and case histories of lake recovery provide the only reliable evidence for policies to reduce eutrophication. The only method that has had proven success in reducing the eutrophication of lakes is reducing input of phosphorus. There are no case histories or long-term ecosystem-scale experiments to support recent claims that to reduce eutrophication of lakes, nitrogen must be controlled instead of or in addition to phosphorus. Before expensive policies to reduce nitrogen input are implemented, they require ecosystem-scale verification. The recent claim that the ‘phosphorus paradigm’ for recovering lakes from eutrophication has been ‘eroded’ has no basis. Instead, the case for phosphorus control has been strengthened by numerous case histories and large-scale experiments spanning several decades.

Limnology in northeastern Ontario: from acidification to multiple stressorsThis Perspective is based on the author’s F.H. Rigler Lecture delivered at the annual meeting of the Society of Canadian Limnologists in Halifax, Nova Scotia, January 2008.

Thousands of lakes around Sudbury, in northeastern Ontario, Canada, were badly damaged by acid deposition and many were also metal-contaminated. Large reductions in atmospheric sulphur and metal emissions have led to widespread chemical improvements in these lakes, and recovery has been documented for various biota. These findings were very important in establishing the necessity and value of sulphur emission controls during the international debates about the effects of acid deposition and the need for cleaner air. Studies of northeastern Ontario lakes are continuing to advance our understanding of chemical and biological recovery processes; however, that knowledge is still incomplete. It has become apparent that the recovery of lakes from acidification is closely linked with the responses to, and interactions with, other large-scale environmental stressors like climate change and calcium declines. Developing a better understanding of lake recovery processes and their future outcomes within such a multiple stressor context will be difficult. It will demand the merging of various approaches, including monitoring, experimentation, paleolimnology, and modelling, and will require effective collaboration among different research and monitoring sites and various agencies and institutions engaged in environmental science.