Freshwater Resources Management

Aquatic Biological Resources Management

Aquatic Biological Resource Issues

Freshwater systems are important reflections of the watersheds in which they are found. They can be characterized based on physical features, water quality, and biological attributes, including species composition, diversity, distribution, abundance, and biomass. Freshwater systems include many types of habitats such as ponds, lakes, seeps, springs, streams, rivers, and wetlands.

In addition to biological community changes resulting from natural environmental and biological processes, aquatic systems can change both physically and biologically as a result of impacts caused by human activities. For example, effects on water quality from contaminated atmospheric deposition or point and nonpoint pollution sources can result in reduced growth and reproductive success, and increased mortality of aquatic organisms. Simple changes in forest cover alter rates of movement of nitrogen, phosphorus, and other important materials in streams and influence downstream habitats. Changing watershed conditions can cause a lowering of the local groundwater table, which concurrently can cause perennial streams to become seasonally dry and a reduction or loss of spring flow. These changes may have far-reaching effects, including loss of riparian and wetland vegetation and associated riparian and aquatic habitat. Habitat destruction on lands adjacent to a park may seriously impact aquatic species if important local portions of species distribution are lost or reduced in reproductive potential, or if such impacts reduce the ability of migrating species to move freely through the area. Introductions of nonnative species also are a potent force in changing populations of native species. Generally such changes are related to competitive interactions for food and space, but can also involve predation. Genetic contamination from hybridization with introduced fish is another important consideration.

A common but subtle form of habitat modification is cultural eutrophication. This process is based upon human-induced increases in the rate of supply of nutrients used in plant growth. Cultural eutrophication occurs when naturally occurring sources of essential growth compounds are supplemented by new sources such as septic tank effluent, soil erosion, fertilizer runoff, domestic animal wastes, landfill leachate, urban runoff, or any point or nonpoint sources that will stimulate plant growth. Park operations can contribute to this process, and training of park staff is appropriate in areas with potential for impacts on water resources and their biota.

The first indications of increased nutrient supply are usually increased algal growth and reduced water clarity. Changes in algal species often accompany new levels of nutrient influx; this species change often influences changes in the zooplankton community, which is composed of very selective algal grazers. Changes in species of zooplankton in turn affect the diet of predatory fish, and so on. Some algae associated with high nutrient environments also exude toxins that further disturb the higher community structure (and can affect swimmers). Odors and extensive vegetation mats are common as are increased weed development in lakes and streams. Dense weed beds preclude swimming, boating, and fishing. Long-term implications are reduced lifespan of affected lake basins and weedy, turbid waters replacing clear-water habitats.

Long-term preservation dictates that great care be taken to limit any activities, operations, or developments that may increase the delivery of nutrients to natural waters and their inhabitants.

Aquatic Resource Management Needs and Actions

Human activities can decidedly alter natural patterns of variation in populations of aquatic biota, producing either artificially luxuriant growth or impaired survivorship. Although changes in some aquatic biological resources may be immediately evident (e.g., fish kills), others occur over many years. A major constraint in protecting aquatic systems is that changes are often gradual, occurring over periods often longer than the usual tenure of superintendents or resource managers. Therefore, a solid inventory and monitoring program coupled with sound documentation and data management practices are mandatory for successful management and preservation of resources.

Inventory and assessment of aquatic park resources

Problems with aquatic resources are usually recognized by loss of some populations or overabundance of others. Generally, little historical information is available, which makes assessment of changes or prosecution for relief from disturbance difficult. Necessary components of prudent management include knowledge and understanding of the range of aquatic biological resources present, and detailed and replicable data (including reference collections) concerning presence and distribution of major species. Information pertaining to the design of inventory and monitoring programs for aquatic biological resources may be found in Inventory and Monitoring in this Reference Manual.

Knowledge of aquatic organism life histories, seasonal cycles, and interrelationships among major species is important to successful management. Vulnerabilities and requirements of each life stage, especially critical events such as spawning, migration, and aestivation, should be known so that current park conditions that might influence species success or failure can be identified.

Structure and organization of natural communities can be altered severely by nonnative species. Many superintendents have inherited a legacy of introduced aquatic species, the impacts of which are little known. Effects of fish introductions may be seen in changes in zooplankton communities, phytoplankton communities (which are grazed differentially by different-sized zooplankton, size being a factor in selection by fish), and macroinvertebrates, as well as in competition with native fish species. Similarly, removal of top native predators (e.g.., by fishing) results in other changes in the community structure (see also Fish and Fishery Resources Management and Nonnative Species Management in this Reference Manual).

Monitoring

Since aquatic biological resources are highly variable, distinguishing natural from human-induced changes requires solid information over long periods of time. Precise measurements of appropriate variables are required, a program that requires diligence, continuity, and sustained management support. Although all baseline data are priceless (in that historic levels can never be fully captured afterwards), great care in choosing species, diversity indices, or general monitoring protocol must be exercised. Frequent analyses of data are required to ensure that information gained meets monitoring objectives and supports management needs. Monitoring generates new understanding and new questions, and can measure results of management actions when implemented.

Impact assessment

Fluctuations in population levels of particular species through death, immigration, emigration, or changes in growth and reproductive success may occur for many reasons. These changes may be natural or human-induced. An impact assessment should include an evaluation of possible causative factors including weather patterns, alterations in physical habitat, changes in land use and management, changes in water quality (including nutrients, suspended solids, toxic chemicals, dissolved oxygen levels/temperature), changes in flow regime, and competition from introduced species. Pathogens may be responsible for, or indicative of, other stresses.

When conducting an assessment to determine the extent of impact of an existing condition or proposed action, the natural resource specialist should take care to provide proper documentation of all observations and events. Further analysis of an impact may require the early involvement of research or technical expertise provided by the park science program, the regional science program, and through the appropriate divisions of the Associate Directorate of Natural Resources Stewardship and Science.

Research

Research can provide an understanding of aquatic biological resources and of the specific roles of individual species in aquatic communities. Information on life cycles and organism vulnerabilities often must be site-specific because of the powerful influence of habitat. Results from intense studies in one habitat may or may not be reliably applied to another. Often applicability of information from one population to another is a matter of professional judgment and sometimes litigation. Site-specific data should be obtained to describe, understand, and protect aquatic biological resources.