Introduction to wetland zonation
Coastal marshes occur at the interface between land and water and support high biodiversity since they contain both aquatic and terrestrial habitats and species. A large number of birds, turtles, snakes, frogs, fish, insects, and mammals use coastal wetlands at some point in their life cycle. Marshes are home to several vegetation types, some of which can only tolerate a short period of flooding, whereas others can tolerate no dessication. Since these wetlands form in shallow, protected embayments, they are also vulnerable to the destructive activities of people, who have built homes and harbours near these protected environments on the shores of the Great Lakes. In fact, >75% of southern Ontario wetlands have been lost since colonial settlement, and majority of the remaining wetlands have been severely altered or impacted by human development.
Coastal wetlands consist of three main habitats: the aquatic portion (low marsh), which is largely flooded throughout the year, the meadow portion (high marsh), which extends from the edge of the aquatic environment to the tree line, and the upstream portion, which comprises forested wetlands that are located above the high-water mark; these upstream wetlands are hydrologically disconnected from the lake but may contribute flow into the wetland periodically (see figure above).
The aquatic and meadow portions alternate their dominance according to the natural 7 to 10 y cycles of water-level fluctuations in the Great Lakes: when water levels are low, submersed aquatic vegetation (SAV) dominate, and when water levels are high, emergent and meadow vegetation dominate. Without this inter-annual variation, either the aquatic or the terrestrial zone would dominate at the expense of the other. This happened recently in eastern Georgian Bay, between 1999 and 2013, when there was a period of unprecedented sustained near record-low water levels. During this period, the emergent and meadow marsh expanded into aquatic habitat, while trees began growing in meadow marsh. By contrast, the aquatic zone became compressed and floating vegetation as well as submersed aquatic vegetation (e.g. pondweed) became very dense because in many cases, the lower boundary of coastal marshes cannot shift lakeward because of their geomorphology.
The importance of good water quality in coastal marshes
Water quality is a scientific term that we use to refer to a number of commonly measured parameters including the ionic properties of the water (conductivity, pH, salinity, total dissolved solids, dissolved macro and micro nutrients), the dissolved oxygen content or physical properties of the water (e.g. temperature, colour), the amount of suspended solids in the water (e.g. reflected by water turbidity, chlorophyll a content, total suspended solids, and Secchi depth) and the level of bacterial contamination. These parameters vary according to wetland geology and geomorphology, as well as the type of human activities in the watershed (e.g. agricultural, urban and industrial development). The amount of nutrients in pristine wetlands tend to be low, whereas in human-disturbed environments, phosphorus and nitrogen levels tend to be elevated due to inputs from manure, fertilizers and sewage. In 2006, Chow-Fraser developed the Water Quality Index (WQI) to assess the level of human disturbance in Great Lakes wetlands based on a suite of 12 water-quality parameters that do not consider bacterial contamination. The WQI allowed us to rank over 150 wetlands throughout the Great Lakes according to the degree of water-quality impairment. A pristine wetland with excellent water quality has clear water, low nutrients and algal growth, and a diverse community of SAV that gives it a score >+2.0. By contrast, a disturbed wetland, with degraded water quality, has turbid water, high nutrients and algal productivity, with low diversity of SAV, (and sometimes none at all) and lots of floating vegetation. Such a wetland would have a score of <-2.0.
This is a photo of a wetland with excellent water quality:
By comparison, this is a photo of a wetland with degraded water quality:
Use of aquatic plants to monitor wetland health
The WQI was designed to allow environmental managers and scientists to monitor wetlands across the Great Lakes basin so that they can track changes in environmental quality through time (positive impacts as a result of restoration, or negative impacts as a result of urban and recreational development). Although the WQI is a good tool, it has several drawbacks as a routine monitoring tool. First, the task of measuring the 12 variables is expensive and time-consuming, and requires specialized equipment and chemical analyses that are not readily available to environmental agencies. This led our lab to develop indices based on the presence or relative abundance in various water-quality conditions. The Wetland Macrophyte Index (WMI) links the presence of certain groups of plants to the degree of human disturbance and assigns a low score (1 or 2) to certain plant taxa that are tolerant of high levels of human disturbance, and a high score (4 or 5) to taxa that are intolerant of human disturbance. The WMI score can range from 1 (highly disturbed) to 5 (pristine), and in practice, a score > 3.25 indicates good wetland conditions. As is the case for the WQI, WMI scores can be treated statistically, and used by environmental agencies to determine if the water-quality conditions in a wetland have changed significantly through time. Alternately, managers can monitor a number of wetlands at one time and compare their quality across the basin.
Compared to the cost and time required to measure water quality directly, surveying vegetation is fast and inexpensive. Even compare with other biomonitoring protocols that use fish or aquatic invertebrates, a plant-based protocol has an advantage because it takes only one field visit per year, when most aquatic plants have flowered (late July to early September), and it seldom takes more than 3 or 4 hours (usually less than 2 hours) to complete a survey, even in a very high-quality site with a diverse assemblage of wetland plants. There is no need to account for seasonality as is the case for fish and invertebrates, and there is no need to have any specialized equipment such as traps or nets. All the equipment required is a canoe, waders, and a garden rake, and an acceptable level of competence in identifying aquatic plants. Tests have confirmed that a WMI score that is representative of a site does not require all species of rare plants to be located and identified. In other words, even if only 60-70% of all plant taxa were identified for a particular site, an accurate WMI score would be generated. This led us to consider developing the Volunteer Aquatic Plant Survey (VAPS) protocol to extend the utility of the WMI so that citizens could participate in long-term monitoring.
Development of the Volunteer Aquatic Plant Survey
VAPS is a rapid-assessment protocol based on the survey method we use to generate WMI scores for wetlands in our research program. In a pilot study, we compared WMI scores generated by experts (Mel Croft and Jon Midwood) with those generated by volunteers from Georgian Bay using the VAPS protocol, and we found no statistically significant differences. Therefore, we are confident that with proper training, volunteers can use VAPS to monitor the health of coastal marshes that they adopt.
Main types of aquatic vegetation in the VAPS
It is important to keep in mind that the VAPS is primarily used to monitor the aquatic portion of the coastal wetland, which is important as fish habitat; therefore, majority of the plants within the meadow and upland portions which are primarily terrestrial are excluded. Plants in the VAPS protocol are grouped into three main categories according to where the leaves and stems appear relative to the water surface, and we have organized the guide to help you identify species according to these three major groups: Floating, Submergents and Emergents.