Extensive literature is available documenting many aspects of wastewater treatment using aquatic plants as sum marized, e.g., by Moshiri , Heavy metal uptake be wetland plants was documented by Simmers et al. , Jamil et at, , Lyngby , Shutes et al. , etc. Examples of storm water runoff treatment using wetlands are less numerous. Among the successful ones we can cite an artificial marsh constructed to remove suspended solids and nutrients from storm water runoff from the city of Tallahassee, FL . Many communities outside California already use constructed wetlands for treatment of storm water effluent. Wetland systems are used for a number of reasons, including low maintenance costs and the potential to combine water treatment with habitat creation. However, regulatory agencies that would permit or comment on the establishment of these constructed wetlands are concerned about the potential for bio-accumulation of urban runoff pollutants. If wetlands are to be used for the treatment of urban runoff, an understanding of nutrient and pollutant cycling within wetland plants during the year is crucial. It will help wetland managers to design proper harvesting schemes for removing pollutants from the wetland environment. While many states and communities have experimented with urban effluent and wetlands to determine the most appropriate plant species and management, little work has been completed in California. Results obtained outside of the state can only partially assist in designing California storm water wetlands as plants, weather,indoor vertical farming and soil conditions differ significantly from those of other states. Consequently, significant interest has been generated in developing a useable information base which would be available to both communities and the state regulatory agencies when making decisions regarding storm water wetland management and design. Another important aspect of this problem is that urban runoff currently drains into existing wetlands, which are protected as waters of the United States by the Clean Water Act.
It is important to know the effects and potential impacts that storm water is or may have on naturally occurring wetlands and to what extent pollutants are being concentrated in parts of plants that will be consumed by migratory or resident animals in the wetland environment. In our project we focused primarily on obtaining data on seasonal dynamics of growth and resource allocation including heavy metals allocation in selected wetland plant species grown under conditions of elevated heavy metals. The obtained results provide a basis for using these species for wetland construction. Hydrocotyle verticillata, Ludwigia pep/oides, Nasturtium aquaticum, Sagitta ria latitolia and Polygonum hydropiperoides, all representing a group of soft and/or creeping emergent macrophytes, and Scirpus ecutus, S. celitomicus. S. robustus, Typha letitolie, T. domingensis and Phragmites australis, representing a group of erect emergent macrophytes. These species were selected because they are native to California with the exception of Nasturtium aquaticum, which is naturalized. According to our previous research and the literature data, they are robust primary producers and posses excellent reproductive capabilities. To obtain data on biomass production, the representative species were sampled at various location in the Central Valley. The above ground biomass was harvested from a 50 x 50 cm quadrat, dried and weighed. The rhizome propagation requires close monitoring of soil water as the rhizome cuttings are highly susceptible to both desiccation and drowning. A greenhouse experiment was carried out to determine the dependence of growth characteristics on water level. Three species, Hydrocotyle verticil/ata, Ludwigia pep/aides and Nasturtium aquaticum were tested. Five different water depth in relation to soil surface were used: -10cm, -Scm, Oem, -scm, and +10 cm, each in five replicates. Individual plants were planted in pots with sand and placed in a large metal container with nutrient solution. Nitrogen concentration in the solution was checked at four day intervals and readjusted to 50ppm. The experiment lasted four weeks, at the end plants were harvested, divided into leaves, shoots and roots, dried and weighed.
To determine the dependence of growth of Hydrocotyle verticil/ata and Nasturtium aquaticum and its tissue nitrogen concentration on the concentration of nitrogen in water, we planted individual plants in 500 ml Erlenmeyer flasks or plastic holders placed in buckets in 1/2-strength Hoagland nutrient solution with 1.4, 7, 14, 35, 70, and 140 ppm of nitrogen added as CaN03′ The nutrient solution was changed every second day. The experiment lasted 25 days.In the second year of the project, four wetlands receiving urban runoff and two control sites were selected for analyses. Two of the runoff retention basins, Octo Inn and Rancho Solano , are located in Fairfield, California, two, the North Pond and West Pond are in Davis, California. A small natural wetland in the Cosumnes River Preserve , together with a marsh at Calhoun Slough at the Jepson Prairie Reserve represent the non-polluted habitats. Plant and sediments were collected in the fall and winter. Water was sampled in January, February and March, 1992, following the rain events. All samples were analyzed for lead, zinc, and copper; sediment samples were also analyzed for molybdenum and cadmium. Metals analysis was conducted using Ionized Coupled Plasma Atomic Emission Spectroscopy . During winter and spring of 1992 a wetland cultivation facility was built in the Putah Creek Reserve area adjacent to the Institute of Ecology, UCD. It includes three sets of fiberglass or plastic containers. The first set consists of 24 round fiberglass tanks . Each tank is divided into four compartments by plywood partitions and filled with soil. These tanks were used for studying the effect of different water levels on the growth of wetland plants. The second set includes 80 small plastic containers that were used for experiments assessing the effect of elevated concentrations of heavy metals on plant growth. Propagules of five wetland plant species, native to California’s Central Valley, were collected in the winter of 1991-1992. Scirpus acutus , S. calffornicus , and Typha domfngensis , were collected and propagated from rhizomes. Ludwigia pep/oideswas propagated from stem cuttings and Sagittaria latifoliawas propagated by tubers. Each plant propagule was planted individually into a #6 nursery pOL Washed sand was used as a substrate. A pot with each species was then put into a large tub and the water level was raised to saturation .
Once the plants had sprouted and established themselves, Hoagland’s nutrient solution, without micro-nutrients, was added and nitrate levels were kept as close to 40 ppm as possible. This was to ensure good plant growth at the time of exposure to the metals. The tubs were then flooded with another 10 L of water to ensure flooded conditions. A randomized complete block design was used for the layout. There were five blocks, each with twelve tubs. Treatments were randomly assigned to the twelve tubs. The four metal salts, mentioned above , were administered at three treatment levels: 0.1, 1.0 and 10.0 parts per million .. There were ten control tubs that had no metals added to the water. Prior to treatment, all plants were measured for length or leaf area. The tubs were treated as batch reactors, according to the design layout. The plants were allowed to grow for an additional two weeks after metal treatment. After this time, the plants were harvested, remeasured, separated into leaves, rhizomes, roots,best indoor vertical garden system adventitious roots, tubers and the original propagule stock. Each part was dried at 80° C for 48 hours and then weighed. Once weighed, the samples were ground and submitted to the University of California’s Department of Agriculture and Natural Resources Laboratory for metals analysis. Metals analysis was conducted using Ionized Coupled Plasma Atomic Emission Spectroscopy . Growth, as a function of biomass increase was determined by using correlations of shoot length to dry weight biomass for Scirpus acutus, S. californicus and Typha domingensis, Stem length and number of branches over 10 cm were used to get relationships for biomass in Ludwigia peploides, and leaf area was used for biomass correlations in Sagitta ria latifalia. These correlation relationships were obtained by destructive sampling in accordance with Vymazal et al. 1993.Evaluating the effect of water level on the growth and biomass allocation of eight species of emergent macrophytes was conducted in the 24 round fiberglass tanks . Each tank was divided into four compartments by plywood partitions and filled with soil. Eight plant species, Scirpus californicus, S. acutus, S. robustus, Typha domingensis, Phragmites australis, Ludwigia pep/oides, Po/ygonum hydropiperoides and Sagittaria latifolia were planted in the late summer of 1992. They were initially kept at the same water level until established, after which, four different flooding regimes, +30, +10, 0, and -20 cm, each in three replicates, were initiated by the end of June 1993. Plants in 40 cm x 40 cm grid placed in each compartment were measured biweekly and the allometric correlations established previously were used for assessing the biomass changes. In September, all the above ground biomass was collected from the grid, separated into leaves, stems, adventitious roots and litter. These plant parts were dried and weighed. In one tank from each replicate, the below ground biomass was collected from the following layers: 0 to -5cm, -5 to -tocrn, -10 to -15 em, -15 to – 25cm, -25 to -35 cm and -35 to -50cm . Below ground harvest turned out to be much more time consuming than expected and teams of people were working on it almost non-stop for 12 weeks. To better quantify standing biomass, obvious features such as stem length or plant height were measured on individual harvested plants and related to the dry weight of each plant respectively. Field recorded measurements of plant height and density can then give estimates of standing biomass over larger areas. We used simple stem length to determine biomass for Phragmites australis, Scirpus acutus, S. californicus and S. robustus. The biomass of Typha spp. was best correlated with a “leaf length index.” This index was calculated as the average length of the four tallest leaves of Typha multiplied by the total number of leaves. Biomass of leaves of Sagittaria fatifolia was determined by measuring the leaf length and width and correlating the index CxD with weight. CxD index showed very close correlastion with the leaf area mesured by the L1COR-L13000A leaf area meter.
The biomass of petioles estimated from the regression of petiole length on its weight was added to leaf biomass. Due to the creeping nature of Ludwigia pep/oides and Po/ygonum sp. allometric correlations were not very accurate. Table 1 presents examples of the biomass and tissue nitrogen ranges for several types of wetland macrophytes from natural habitats. The time course of decomposition for of some of these species is shown in Fig. 4. The survey of heavy metals in water from several runoff retention basins sampled in January, February and March, 1992, following rain events did, not reveal any increased metal concentrations. Except for Zn, no detectable levels of heavy metals were found in water samples. Of the plant samples from polluted sites, Nasturtium aquaticum was found to contain the highest levels of Zn . Surprisingly, Sagittaria latifolia from Cosumnes Preserve, our control site, also contained high levels of Zn. If we divide all the plant species tested into two groups based on their growth form, t.e., erect emergent macrophytes and creeping emergent macrophytes, the group of creeping macrophytes, represented by species such as Nasturtium aquaticum, have significantly higher levels of Cu and Zn in their tissues than does the group of erect emergents . Heavy metal concentrations in sediments were not as high as we expected; samples from Octo Inn Basin showed the highest levels of plant available Zn, Pb and Cu among the “polluted” sites. Sediments from the Cosumnes Preserve had the overall highest metals concentrations . However, the levels of lead were generally quite low at all sites. The heavy metal content in plant biomass was not correlated with the concentrations of individual elements in sediments. While the Cosumnes Preserve sediments had the highest concentrations of metals, the highest metal concentrations in plants were found at Rancho Solano. Cadmium is one of the major environmental pollutants and a potential hazard to worldwide agriculture.