APIS - Ecology

Introduction--Recommendations

Aquatic plant quantification is not as well developed as water chemistry analytical procedures or public health sampling. A unified procedure for determining either the proper number of samples or methods to follow, has not been developed by the USEPA. These topics are also not adequately covered in Standard Methods for the Examination of Water and Wastewater (Clesceri et al. 1989). There are no required aquatic plant quantification procedures for the USEPA Clean Lake Program projects, even those involving aquatic plant control, although an extensive program of water quality sampling and water analyses are required. Therefore, making recommendations on necessary sampling is without previous benefit. Some allowance must be made for the amount of funding available for the program, the size of the lake, and other variables. In addition, all sampling need not be done every year, but more intensive quantification efforts can be alternated with less intensive monitoring.

Information Needs

Species List

The most basic information needed to manage lake vegetation is a comprehensive list of species. Species surveys are necessary both to search for exotic, potentially nuisance-forming species as well as detecting the presence of rare and endangered species. The presence of either class of species will alter the management mode in the lake. Exotic nuisance species would require more intensive surveys to gather information appropriate for planning management alternatives, and the exact distribution of rare plants might need to be studied to avoid destroying them during management applications or as required by permitting agencies.

Before exotic nuisance species invade a lake, management of the lake's vegetation should focus on preventing the introduction of nuisance species by posting warnings at all boat launches (Photo 1), monitoring all access point, and educating the public. Periodic species surveys should be done to watch for early growth stages of nuisance species. This might be done by a citizen plant watcher's program. The best practice would be periodic (every 3 to 5 years) surveys by trained technicians, either using a diver swimover or transects, with a citizen's plant watcher's group doing annual monitoring of shallow embayments and public access points. At a minimum, lay persons should be enlisted to patrol boat launches and look for suspicious plant growths.

Photo 1

Nuisance or Exotic Species Plant Distribution and Abundance

One nuisance exotic species are found in a lake, more intensive monitoring is needed to gather adequate data for making management decisions. Detailed information on exotic species abundance and distributions and locations within a lake are needed to choose among management alternatives. Also, more extensive information on native species, particularly rare and endangered species, may be required by permitting agencies. Therefore, a minimum of an organized citizen plant watcher's program or comparable activity is needed to gather information on the extent of exotic species within the lake each year. These annual lay surveys should be supplemented with surveys by trained technicians every three to five years, in the form of the diver swimover surveys. These surveys are to verify citizen's data, and to evaluate changes in native plant status over time using at least a semi-quantitative format.

The best monitoring practice would consist of a citizens' plant watcher or plant ID program, using casual or trained citizens to supplement the efforts of trained technicians to locate new sites of exotic species. The trained technicians should survey known sites each year, evaluating the extent of nuisance plant growth and semi-quantitatively evaluate exotic species abundance, such as using echolocation devices to measure plant height or biovolume (see Madsen, 1992). In addition, diver swimovers should be used to monitor plant communities at selected sites each year, and a program of evaluating sites at risk, such as shallow embayments, popular boating sites, and boat launches, should be implemented. Additional quantitative data for monitoring purposes on larger lakes should also involve annual remote sensing surveys to indicate the extent of nuisance growths, if this technique is practicable. Lastly, monitoring the entire plant community change over time should include transect-type quantitative surveys at least every 3 to 5 years. These surveys should be more frequent early in a monitoring program, with intensity decreasing as time progresses. These surveys will help assess changes over time in the plant community, including the abundance of exotic nuisance species. Transect studies might involve permanent transects or structures (Madsen et al., 1991) or randomly located transects perpendicular or parallel to shore (see Titus, 1992 and also Chapter III).

Management Tactic Assessment

TThe assessment of a management tactic should include both an economic and a biological assessment of effectiveness or efficacy. An economic assessment is best done by maintaining precise records, such as harvesting logs, on the cost of labor, equipment and maintenance. These costs should be compared in an equitable fashion. If there is a discrepancy in the amount of required monitoring between two methods, this should also be included in the evaluation. For example, an application of an herbicide might require analysis of water samples for herbicide residue, which should be included as a monitoring cost. Lastly, any impairment to the use or quality of the resource should also be considered. For instance, applications of most herbicides require drinking water, swimming and recreational restrictions. If supplemental drinking water or loss of revenues from swimmers or fisherman is expected, these should be considered in an economic analysis.

The biological or "control" effectiveness of a management tactic should be considered based on the amount and longevity of a reduction in plant abundance. A minimal sampling program should consist of trained technicians surveying the site, evaluating the effect of treatments on native and exotic species utilizing at least a semi-quantitative approach. For longer term treatments, transect surveys of the sites using permanent transects or biomass evaluations should be done at leat every 3 years. These assessments should compare the treated area to a non treated reference area, to compensate for interannual variations in plant populations. br />
TThe best monitoring and assessment approach should include trained technicians evaluating the treatment sites every year. For most management tactics, the best plant quantification approach would be biomass sampling before, immediately after, and at extended periods after treatment to monitor both the immediate impacts of the management tactics, as well as the long-term effectiveness and regrowth rate. These efforts are best performed at several sites, both multiple treatment and non treatment sites. If a particular management tactic is to be evaluated to test for intensity of approach, several replicates of each treatment level, in addition to replicates of the reference area should be evaluated. In addition to plant monitoring, appropriate environmental measurements should also be performed as relate to the direct environmental impacts of a given management tactic. For instance, the effect of dredging on water quality and transparency may need to be evaluated if resuspension of sediments is an issue of concern by the permitting agencies or lake constituents.

Assessment of Specific Management Tactics

As with monitoring native or newly invaded lake littoral communities, room must be left for individual creativity in developing plans for assessing management tactics. Therefore, the following should be treated as suggestions or guidelines rather than as sampling prescriptions. The important point is that assessment should involve rigorous quantitative methods that can give a statistically meanignful answer to the question, "Did the management tactic succeed in reducing the exotic nuisance species' growth?"

Chemical Control

A minimal sampling effort associated with herbicide application to control aquatic plants should be a transect study involving at least one treated site and one reference (untreated) site. This sampling program is mostly geared towards indication the impact on native plants and, to a lesser extent, the abundance of the target species. Biomass sampling is always preferable in assessing control tactics, so this would be the next step in improving sampling design.

The best approach involves quantifying biomass at two or more sites each of two or more levels of chemical treatment, and at least two reference sites. These sites should be studied before and after application, and during the regrowth period (Photo 2). Spencer (1992) gives additional details on setting up such a study.

Photo 2

The label recommendations on herbicides are based on the allowed toxicity standards, rather than on what is sufficient to provide adequate control of plants. The amount or concentration of herbicide needed for control varies with conditions, and is based predominantly on the concentration versus exposure time relationships between the gerbicide and target species (Westerdahl and Getsinger, 1988; Netherland et al., 1991). Therefore, specific studies of application rates on a pilot scale may both ensure adequate control and potentially reduce the amount of herbicide required, both saving money and reducing potential environmental impacts.

Harvesting

The minimal monitoring effort for harvesting or other mechanical controls would involve a quantitative transect survey at both a treated and reference site before and after implementation, to monitor the effect on the target and native species. As with chemical control, measurement of biomass is preferred to cover transects in terms of assessing reduction in abundance (Madsen, 1992). The best approach would be to monitor at least two reference sites, as well as two or more sites each of successive harvest frequencies or patterns (Madsen et al., 1988a; Madsen, 1992). Varying harvest frequencies in some fashion other than "when it gets long" (like the lawn) may actually improve the effectiveness of harvest as a long-term control technique. Some studies indicate that intensive harvesting repeated several times per growing season over consecutive growing seasons may actually reduce plant growth over many years, while harvesting once or twice per season may actually stimulate growth (Nichols, 1974; Westlake and Dawson, 1982).

Drawdown

Drawdown is an extremely effective control technique for some species, while it may actually stimulate the growth of other species. Species changes can be expected in years subsequent to a drawdown. The minimal approach to monitoring drawdown is to monitor quantitative transects in target plant regions in the growing season before and after drawdown. Permanent transects would be especially appropriate in this instance. The best assessment effort would be to quantify biomass at several sites in growing seasons before and after drawdown. This type of quantitative method was used to measure the spread of Eurasian watermilfoil in Lake George (Madsen et al., 1988b) as well as assess the impact of this species on native plants (Madsen et al, 1991), and should be quite amenable to studying revegetation.

Benthic Barrier Benthic barrier is possibly the least selective control technique used, and also the most easily controlled in application. Examining revegetation is particularly important at these sites and , since benthic barriers are generally applied to small areas, these sites are also more easily revegetated or monitored. In many instances, a benthic barrier is applied and left in place permanently. In these cases, divers should inspect the mat annually. If the mat is to be applied and removed after control is affected, a monitoring effort should be undertaken. The minimal effort should be to assess transects or permanent plots in the treated and untreated areas before and after application. The best approach is to quantify biomass at several reference and treated sites before and after application, as well as monitoring during regrowth. In addition, permanent grids could be used to monitor revegetation or investigate the ease revegetation directly (see above).

Nutrient Removal

Nutrient removal from the water column has had minimal effects on rooted aquatic vegetation, at best. However, some work has been done on immobilizing sediment nutrients through injecting alum or other phosphorus binder into the sediments. Since sediment nitrogen has been recently implicated as a factor that limits rooted submersed aquatic plant growth (Anderson and Kalff, 1986), a new tact on this approach might be tried. In such an experimental approach, at minimum the program should involve monitoring water and sediment nutrient availability and either transect abundance or biomass quantification. The best approach would perform the monitoring at several treated and untreated sites, using biomass to quantify the effectiveness of the control tactic.

The above constitutes a series of recommendations on the general form of a long-term monitoring effort, as well as recommendations for specific control efforts. By no means should monitoring become the bulk of the cost in a management program. Rather, monitoring and assessment is performed to evaluate the usefulness of each management tactic. In the long run, monitoring and assessment will become cost-effective in saving money on expensive tactics or chemicals, as well as in increasing the ability to make intelligent management decisions.