Search Results

Reanalysis of previously published data on trends in sedimentation rates over time in eight small lakes in the northern range shows variations associated with elevation and character of lake basin (kettle lakes or lakes in slide-deposit terrain) that must be taken into account in evaluating whether sedimentation rates have changed over time in response to increases in the elk herd. Total sedimentation rates and those of allogenic silica increased in most lakes between park establishment and the 1980s-1990s. Total organic sedimentation rates, and those of biogenic silica and phosphorus, increased during park history indicating eutrophication. Two species of diatoms characteristic of eutrophic conditions increased during park history in three of five lakes. Although more comprehensive research is needed on this question, an increase in the northern herd is the most probable hypothesis to explain the evidence from this preliminary study.

This chapter describes some approaches for understanding biodiversity-ecosystem function at larger spatial and at longer temporal scales. It first considers the importance of building a credible evidence base of biodiversity change effects on ecosystem functioning at seascape scales. It then explores the different aspects of biodiversity change, compositional and species richness, within contrasting bottom-up controlled and top-down controlled systems, namely, estuaries and coral reefs. The two systems are affected by eutrophication and overfishing.

This chapter examines changes in aquatic communities. Key threats to lake plant communities include shoreline development, heavy boat traffic, nutrient runoff, and consequent lake eutrophication and turbidity. Many invasive species capitalize on these conditions, forcing more elaborate efforts to control the excessive growth of invasive lake plants and algae. Lake plant communities also sometimes surprise scientists, as when a previously degraded community recovers beyond what we might expect.

Although current understanding of the sources, fate and impacts of many contaminants are now well-known and regulated by national and international bodies and conventions, a number remain problematic. Some are produced in very large quantities (e.g. nutrients, detergents, oil) and others are persistent in the environment (e.g. radioactivity and plastics). All are known threats that have either been ignored, took time to manifest, or have been challenging to manage. For most of these pollutants, regulations exist but changes in the nature (e.g. microplastics) or scale (e.g. increased use of fertilisers, increased livestock culture and sewage production, and changes in energy consumption as the global population grows) may mean existing regulation or management is in some way deficient. For others, (e.g. radioactivity, plastics and threats to biosecurity such as non-native invasive species introductions) the challenges associated with regulation and management are yet to be solved.

Seven regions are described in terms of their pollution history, other synergistic human pressures, the current challenges and management approaches. Although the timing and detailed impacts vary, primarily for historical reasons, between regions all show similar patterns of change. Sea regions exposed to centuries of human activity (North Sea, Black Sea, Mediterranean Sea and Chesapeake Bay) are considered, as are those for which pollution is more recent (Canadian LOMAs and Coral Sea), and those expected to experience intense pressure in the near future (Arctic Ocean). Nutrients from agriculture and sewage from growing human populations are ubiquitous and not easily managed in marine systems. Controls on industrial discharges have succeeded in halting, sometimes reversing, degradation in some regions (Black Sea, Mediterranean, North Sea, Chesapeake Bay). However, shipping, coastal development and offshore infrastructure continue to apply pressure. While most regions are subject to international agreements and management regimes the effectiveness varies.

The last chapter of Lakes and Ponds deals with how human activities affect the natural ecosystems and their function through eutrophication, contamination, acidification, brownification and increases in UV radiation, and how such anthropogenic disturbances may affect biodiversity and the ability of organisms to utilize a specific habitat. In addition, the chapter addresses novel environmental threats, such as global climate change and effects from our everyday chemicals, such as contraceptives, nanoparticles and antidepressant drugs. However, also possibilities and signs of improvement are discussed, providing hope for coming generations.

Marine organisms can experience conditions ranging from limiting supply of nitrogen in open ocean regions to toxicity of high concentrations of nitrogen associated with coastal eutrophication. Photoautotrophs show physiological acclimation to low N stress and relatively high tolerance to variable elemental stoichiometry. Symbioses and associations can help overcome low N supply in a range of ecosystems. Stress due to N limitation was once regarded as more ecologically relevant but increasing anthropogenic N loading is resulting in more common stress to photoautotrophs due to high N concentrations, especially for coastal benthic macrophytes. High N also affects competitive interactions between functional groups such as corals and macroalgae. Heterotrophs are less flexible stoichiometrically, and N supply and use is coupled more tightly with energy supply through catabolism of organic (food) molecules, releasing nitrogenous wastes. The responses of mixotrophic organisms to low or high N stress are poorly understood but N status can affect toxin production in harmful algal bloom species. In all groups, larval and recruiting life stages may be more sensitive to N stress, particularly high ammonium and nitrite toxicity. Identifying N stress increasingly uses molecular biological approaches but correct interpretation of such data requires a better understanding of the physiological effects of N stress on marine organisms.

This chapter gives a broad overview of freshwater algae in standing (lentic) and flowing (lotic) waters, with information on their morphological and taxonomic diversity. Algal communities are considered in relation to phytoplankton, substrate-attached and biofilm organisms. Methods are given for their collection, sample processing, enumeration, and biomass estimation in different aquatic situations. The relevance of these algae to human activities is considered particularly in relation to eutrophication of standing waters and the occurrence of harmful algal blooms. Control strategies to limit the growth of colonial blue-green algae are discussed within the context of an integrated management policy

This chapter describes how phosphorus is used in biological molecules, structures, and physiology. It illustrates the role of phosphorus as a limiting nutrient for the production and growth for organisms and ecosystems. It also explains how phosphorus cycles in natural and agricultural ecosystems cause aquatic eutrophication of downstream surface waters.