Restoration and Phytoremediation in Two Impaired Hawaiian Streams Using Native Plants and Coir Fiber Logs.
Carolyn Unser
M.S. Thesis Proposal
Advisor: Dr. Greg Bruland
Department of Natural Resources and Environmental Management
Summer 2008
Abstract
Many of Hawai’i’s streams are currently on the State’s 303(d) list of impaired water bodies for which nutrients, turbidity, and suspended solids exceed that of Environmental Protection Agency (EPA) allowable loads. Waimānalo Watershed, a Category I watershed within the Ko’olaupoko region of Oahu, is listed as a top priority watershed for restoration. In response, reports such as the Total Maximum Daily Loads (TMDL) Estimated for Waimānalo Stream and the Waimānalo Stream TMDL Implementation Plan were developed to document current conditions and control methods. This M.S. Thesis will address issues raised in these reports by applying one of their suggested best management practices (BMPs), phytoremediation, in order to increase nutrient uptake by riparian plants and to enhance stream structure and function. Due to the highly episodic flow periods common to this area, existing demonstration projects have been challenged by the task of establishing and maintaining stream bank vegetation. An innovative approach using native sedges planted in coconut coir logs and installed along stream riparian zones will be studied in an experimental setting and then in a large-scale field installation along sections of Waimānalo and Kahawai Streams. Similar methods to establish riparian vegetation have been used on continental streams but their use has not been documented on Hawaii's streams. Identification of appropriate species for remediation and successful installation of pre-planted coir logs along stream banks will protect sedges from high flows and accelerate root anchoring into stream-bank substrate as the logs degrade. The main hypotheses to be tested are as follows: (1) native wetland/riparian plant species will be able to successfully establish and survive in coconut coir media; (2a) individual species selected will have significantly different levels of tissue nitrogen (N) content when exposed to varying levels of N; (2b) within species, tissue N content will increase across the N addition treatments; (3) pre-planted coir logs will have a higher degree of % cover than direct plantings; and (4) installation of coir logs will decrease nutrients in stream waters as planted species will uptake nutrients.
Literature Review
Introduction
Waimānalo Watershed, located in the Ko’olaupoko District region of Eastern Oahu, drains about a 16 km2 area into Waimānalo Bay and onto a reef with submerged margins (KBAC, 2002). Waimānalo Stream is the primary drainage for the basin valley and the watershed’s only true perennial stream which stretches about 5.5 km in length. The stream is in the shape of the letter “Y,” with the southeastern tributary identified as Kahawai Stream and the northwestern tributary, named Waimānalo Stream. Unless otherwise noted, the term “Waimānalo Stream” includes both Waimānalo and Kahawai tributaries (KBAC, 2002). Waimānalo translates to potable or sweet water in the native Hawaiian language (Pukui, 1986). Waimānalo Stream, however, was described in a recent report issued by the Hawai’i State Department of Health (DOH) as an impaired, highly-altered waterway that no longer functions as a natural stream, since sediments and nutrients from the watershed enter the stream at a rate faster than they can be assimilated and recycled (HDOE, 1998; Harrigan, 2001; KBAC, 2002).
Waimānalo Stream was listed as an impaired water body on Hawai’i’s 1998 Clean Water Act 303(d) List (KBAC, 2002; HIDOH, 1998). In a standard response to the official priority listing, a Total Maximum Daily Load (TMDL) assessment for Waimānalo Stream’s was conducted. This assessment, prepared by the DOH, determined the maximum amount of pollutants that can enter Waimānalo Stream without violating the State’s Water Quality Standards, compiled in the Hawai’i Administrative Rules, Chapter 11-54 (Harrigan, 2001). Following this assessment, a report for implementation recommendations was ordered. This report described Waimānalo Stream’s many problems, including poor water quality, lack of habitat, and altered flow regimes. Since placement on the EPA’s 303(d) list of impaired water bodies of Hawai’i, residents and environmental interest groups have recognized the need for restorative action and the need to address the point and nonpoint sources effecting health of Waimānalo stream.
Many factors have contributed to the decline of this stream system. Urban development and land-use changes over the last century have drastically altered this streams waterways and landscapes resulting in a shift of natural system functions and processes (Laws, 2003; KBAC, 2002). The streams in the watershed are prone to flash floods and prolonged periods of low flows (Tomlinson, 2003). Erosion of stream banks, including the toe area, is one of the major contributors to sediment pollution problems in streams and near shore marine waters of Hawai’i. Other contributors of stream pollution include surface runoff generated from anthropogenic sources such as cess pools, leaching of agricultural and residential fertilizers, and animal waste. These pollutants are then transported along the waterways where they are either deposited in or along the streams or in receiving waters at the ocean. Land-based sources of pollutants, such as sediment, nutrients, and other pollutants, are one of several factors threatening the quality of coral reef ecosystems in Hawai`i (EPA, 2001 and 2004). Management of these identified stream problems is important for sustaining Hawai’i’s terrestrial and aquatic habitats, as well as, ensuring the future of healthy aquifers.
Past demonstration projects with this stream have employed bio-engineering techniques for the protection of stream banks. This project will build upon past remediation efforts and utilize principles from constructive wetlands for nutrient uptake. The use of coconut coir fiber “logs” for toe protection will be expanded to include the development of pre-planted logs that will decrease the time that the vulnerable area of banks are exposed to erosion during restoration projects. Successful establishment of vegetation in the toe area can significantly decrease sediment loads generated from these areas during storm flows (EPA, 2001). Riparian plantings often act as a sink for nutrients from runoff waters because they can remove nutrients entering streams through surface and subsurface soils (Sabater, 2000). Native plantings will replace alien vegetation that decrease stream habitat and often clog channel ways (Laws, 2003). Although pre-planted logs have been successfully used in the continental U.S., this technique has neither been demonstrated with Hawaiian plants nor under the highly variable flow rates found in Hawai’i.
Phytoremediation of nutrients in Waimānalo and Kahawai Streams takes advantage of the natural metabolic processes in living plants to carry out a variety of chemical reactions that are energized by sunlight. Plants and associated microorganisms can absorb, transform, or degrade pollutants, thus limiting their spread in the environment. To understand the role of these plants in the treatment process, it is important to consider the role of phreatophytes[1] in the landscape. Phreatophytes are only one part of a complex system, so when comparing the effectiveness of a system process, such as reducing organic N, performance considerations of the complete system must be taken into account.
The process of utilizing plants for the cleanup and containment of nutrients contained in the free flowing water of streams in Hawai’i warrants further research. There have been studies focusing on the effectiveness of constructed wetlands or riparian zones in Hawai’i using native plants. However, few studies have quantified individual species and their effectiveness in remediating nutrients, metals, or other types of pollution. To date most “restoration” in Hawai’i has simply involved removal of non-native, invasive vegetation. A review of the scant literature regarding wetland restoration in Hawai’i has established that learning how to effectively restore native plants to Hawai’i’s streams will require much more effort, scientific study and most importantly, documentation of successes and failures encountered when attempting to restore wetland vegetation (Brimacombe, 2002).
This project will conduct nutrient loading experiments with several native Hawaiian sedge species planted on coir logs, document their ability to take up nutrients, grow out the most effective plants in coir logs at a greenhouse, and conduct a large-scale field installation of these pre-planted coir logs at the toe of the stream banks of Waimānalo & Kahawai streams. Field data collection will document success of implementation and restoration of stream ecological structure and function. Changes in water quality parameters (e.g. nutrient concentrations) and plant survival through different installation methods, such as pre-planted coir logs or out-planting potted individuals will be monitored over the course of the thesis research.
Objectives and Hypothesis
Overall Objective: To identify candidate native sedge species for stream phytoremediation and to demonstrate the use of pre-planted fiber logs for successful plant installation in two Hawaiian streams.
Experimental Objectives and Hypotheses
Objective 1: Select and test native wetland/riparian plant species [Cyperus javanicus Houtt, Java sedge (Ahu’awa), Cyperus laevigatus L., smooth flatsedge (Makaloa), Cladium mariscus ssp. jamaicense Crantz Kukenth, sawgrass (‘Uki), and Cyperus polystachos. manyspike flatsedge (Kiolohia) for their suitability for restoration at a demonstration site using a set of pre-determined criteria.
Objective 2: Determine success of using coconut coir logs as a media for plant root establishment prior to field installation.
Alternative Hypothesis 1: Native wetland/riparian plant species will be able to successfully establish and survive in coconut coir media.
Objective 3: Expose selected species to varying levels of N (in the form of ammonium nitrate in surface water) and compare their tissue nutrient uptake.
Alternative Hypothesis 2a: The individual species selected will have significantly different levels of tissue N content as biomass structure, physiological needs, and nutrient tolerances differ among species.
Alternative Hypothesis 2b: Within species, tissue N content will increase across the N addition treatments.
Field Establishment Objective and Hypotheses
Objective 4: Install and secure pre-planted coir logs along 92 meters (m) of each stream and monitor plant species survival and compare species percent (%) cover and planting method success.
Alternative Hypothesis 3: Pre-planted coir logs will have a higher degree of % cover than direct plantings.
Objective 5: Monitor quarterly water quality samples from streams, including N (nitrate, ammonium, and total dissolved N, phosphorous (P), before, during, and after coir log installation.
Alternative Hypothesis 4: Installation of coir logs will decrease nutrients in stream waters as planted species will uptake nutrients.
Methods
Plant selection
The selected plant species have been repeatedly mentioned in literature related to constructed wetlands or have been used in erosion control projects in Hawai’i, and/or have been recommended by experts in the field. Persons contacted about plant selection include the following: Matthew Kanemoto (Kahuku High Agricultural Science Program Director), Pauline Chinn (UH Mānoa Professor, Education and Curriculum Studies; Science Multicultural Education, Indigenous Science Curriculum), Dennis Kim (Native Plant landscape Nursery Owner), and Hui Ku Maoli Ola Nursery (Native Hawaiian Plant Specialists). Species have been chosen which meet the project criteria:
1. Native status
2. Wetland indicator status.
3. Potential ability to establish roots within and grow on coconut fiber coir logs
4. Pollutant uptake
5. Stream hydraulic properties
6. Ease of maintenance.
7. Remediative quality/attached microbial growth on root
8. Commercial/Local availability.
The species selected will need to thrive in the existing impaired environmental conditions of Kahawai and Waimānalo Streams. Baseline samples will be collected and used to characterize the in-situ site conditions that will need to be represented in the greenhouse study in order to ensure success of field plantings.
Four species of native Hawaiian wetland plants will be exposed to different concentrations of N though a cyclical hydroponic system established outdoors at the CTAHR Mauka Campus experimental plots. The four species selected are: Cyperus polystachyos (Kiolohia), Cyperus javanicus ('Ahu'awa), Cyperus laevigatus (Makaloa), Cladium jamaicense ('Uki).
Growbox Sampling Design
The plants will be planted in coconut fiber coir logs that will be placed into 6 mm plastic-lined wooden grow-boxes with the dimensions 2.5 m x 1.2 m x .46 m. An irrigation reservoir will be hydraulically connected to the grow boxes. The grow boxes will have a slightly positive slope and at the low end a 227 Liter per hour aquarium pump will convey effluent water to a catchment reservoir, which will return the water to the irrigation reservoir. Three grow boxes will be used, each with four coir logs, measuring 2.13 m by approximately 20 cm diameter, placed in each grow box. Plants will be positioned in a randomized complete block design to minimize effects from position, distance, shading, or species interaction. Blocks can be defined either by plant distance on each log from irrigation reservoir or by each log itself (Appendix 1).
A hydroponic fertilizer will be added to the irrigation reservoir as a baseline nutrient solution for optimal plant growth. In addition to the baseline solution, ammonium nitrate will be added to increase the aqueous nitrate in the second and third boxes by 4 mg/L and 8 mg/L, respectively, above baseline additions to reflect a high and very high range for the stream. Ammonium nitrate quantities for grow box additions were determined by comparing results from the project’s September 2007 stream sampling and from data contained in publications of past sampling analysis and recommendations regarding Waimānalo and Kahawai Stream sampling (Harrigan, 2001; Laws, 2003). Physical and chemical properties, such as pH, temperature, etc., will be closely monitored to ensure no major differences.
Grow box water will be changed and both the baseline hydroponic fertilizer and the ammonium nitrate additions re-administered every two weeks. Samples will be analyzed for total dissolved nitrogen (TDN), nitrate+nitrite (NO3+NO2), total phosphorus (TP), and phosphate (PO4-P). Quality Assurance/Quality Control water samples will be collected (1) 24 hours, and 2) 1 week following the addition of baseline and spike nutrients) on a minimum of two occasions; these samples will also be sent to the Marine Science Analytical Lab (MSAL) at UH Hilo for analysis. The 24 hour sample will be used to measure the efficacy of the estimated computation of initial N and P concentration derived via mass volume calculations and the 1 week sample used to estimate if nutrient uptake by plants is linear.
The final month of the experiment trial will consist of deconstructivly harvesting and measuring the biomass of each species from within each nutrient treatment for estimates of the aboveground biomass. Sampling of 2 or 3 plants per nutrient level will, decided at time of harvest, will allow for a replicated design of analysis. Plant biomass weights will be compared within species for differences and between nutrient levels.