Field-testing the HGM wetland function models

How healthy or undisturbed is a wetland? What effects will a development have on a wetland? How can we tell? In 2001 the Division of Environmental Quality (DEQ) in conjunction with the Environmental Protection Agency (EPA) and the Army Corps of Engineers (ACOE) produced a draft manual called “Hydrogeomorphic (HGM) Functional Assessment for Depressional Wetlands of the Commonwealth of the Northern Mariana Islands”. Whew! That’s a long title! But in short, the manual explains how we can determine what services an individual wetland provides. As you may remember from earlier articles on this page, wetlands provide habitat for fish and birds, they filter storm water and can remove harmful contaminants and sediments from the water before it reaches our coasts, and they are an integral part of the water cycle. The manual outlines several models to assess these functions. They are: habitat (what flora and fauna exists in or uses the wetland), biochemical (how pollutants, sediment, and other minerals and organics are processed and removed from water by the wetland), and hydrological (water flow in and out of the wetland and where it goes). We can use these models to assess the services provided by a wetland of interest; for example, one that has been impacted by development. If we compare these to the services provided by a healthy or undisturbed wetland, we can see how the wetland of interest has been or might be impacted. Again, as you may recall from an earlier article, since wetlands are protected under the law, if anyone wants to harm them, they need to make up for their lost functions by creating new wetlands or enhancing existing wetlands. This is called mitigation. Managers need to know what functions are going to be lost to development or other activities in order to determine the required mitigation. That, in short, is the point of doing an HGM assessment.

The CNMI has eight reference wetlands used in the HGM Manual. Seven are on Saipan and one is Hagoi, in the Unai Chulu area on Tinian. Until last week, no one had tested the models of the HGM Manual to see if they were able to estimate the general condition of an existing wetland compared to the reference wetlands, or if the models would allow wetland managers to predict how development or filling of wetlands might affect their functions. So, the Coastal Resources Management Office, with financial assistance from the National Oceanic and Atmospheric Administration (NOAA) and EPA, hosted a field testing of the HGM Manual. Several CNMI wetland management agencies, including DEQ, Tinian’s Department of Lands and Natural Resources,the Marianas Public Lands Authority, Department of Public Works, as well as private consultants participated in the field trials.

Mary Butterwick of EPA Region 9 led the trials with the assistance of Robert Carruth (CNMI United States Geological Survey Hydrologist), Dr. Robert Gavenda (Guam Natural Resources Conservation Service Soil Scientist), and Frank Dayton (Guam US ACOE Wetlands Expert).

The first day of the testing was spent in the CRM conference room, getting familiar with the draft HGM manual. Participants reviewed two fictional developments created to field test the models. One of the fictional developments was set in the Susupe Lake Marsh, and the other was in the Chalan Lau Lau wetland. Participants were split into two teams and used the manual’s models to calculate the “pre-development” function of the wetland. In other words, what functions did the wetland provide before development took place? The next two days were spent in the wetlands determining how these two wetland habitats would be affected should the proposed fictional developments take place.

The teams found that with some more refinement the HGM Manual models may be useful to wetland managers and developers. This model is especially important since wetlands are currently assessed mostly for habitat functions, and hydrological and biochemical functions are only rarely taken into account when determining mitigation.

However, much more work is needed before the HGM Manual would be considered for adoption by government agencies. Mary Butterwick is working with the editor of the draft HGM manual and other leads that assisted with the field testing to provide recommendations for refining the manual. It is hoped that a finalized HGM Manual will help wetland managers and developers to properly prepare for and/or assess environmental impacts and therefore more fully restore or mitigate all wetland functions, resulting in a no-net loss of wetland utility in the CNMI.

If you would like more information about wetlands and the HGM Manual please contact Kathy Yuknavage at 664-8300/1.

CoCo