One of the amazing aspects of GIS is the ability to combine information about multiple topics from multiple time periods and from multiple sources into one place and then analyze them spatially. There are tradeoffs to consider for this convenience. As we saw in Lesson 2, before you can use data that you did not create yourself, you need to invest a great deal of time to acquire and understand each dataset. The more data sets you include, the more time you need to spend on these tasks. After you have acquired and understand your input datasets, you still need to customize them for your project. Other time-consuming tasks include interpreting the results of your analysis and figuring out how to best communicate them to your target audience. The analysis itself can be the quickest part – you typically just need to click a few buttons and wait for a GIS tool to run.
Customizing data for your project involves two main tasks: 1) modifying your input datasets so that they are consistent enough to combine them in spatial analysis and 2) modifying them so that they can answer your specific questions in your study area. The specific sub-tasks can be grouped into two main categories: spatial tasks and attribute tasks. It is better to address spatial issues first since you will likely add or remove records from your attribute tables in the process. Examples of each type are described below:
Spatial Tasks | Attribute Tasks |
---|---|
Convert Data Format | Understand Coded Values |
Resolve Projection / Misalignment Issues | Recode Missing Data |
Customize Data Organization | Recode Typos |
Correct Topology Errors | Reclassify Attributes |
Modify Extent | Create New Attributes |
Confirm Scale | Convert Units |
According to ESRI, project on-the-fly in ArcGIS works better for vector data since the process of projecting rasters on the fly is so much more complex than projecting vector data. Projecting data on the fly, regardless of whether the data is vector or raster, does not always produce consistent results. Sometimes, it works perfectly; other times, it does not. You can read more about it in this Esri Blog Post, "Projection on the fly and geographic transformations [1]"
What are wetlands? Wetlands can be broadly described as transition zones between water and land. They are notoriously hard to define because their characteristics vary greatly depending on their location and the environment in which they are located. One trait all wetland varieties share is that they have properties of both upland and aquatic environments that create unique ecosystems.
Wetlands are important for several reasons. First, they support a vast array of life with biodiversity and population counts comparable to tropical rainforests and coral reefs. For example, they are used as nesting and feeding grounds by many species of migratory birds, and most fish and shellfish are dependent on wetlands for some portion of their lifecycle. Second, wetlands help regulate the flow of water over large regions. During extremely wet periods, wetlands absorb and store excess water, preventing floods and associated damage. Third, wetlands help to recharge groundwater aquifers, a source of drinking and irrigation water, during times of drought when rain is scarce. Fourth, wetlands help to filter and clean water. As water enters a wetland, its speed is drastically reduced, mitigating possible erosion of valuable soils. Reducing water speed also causes suspended and dissolved particles, such as pollutants and nutrients, to drop out of the water when they enter a wetland. Plants and microorganisms living in the wetland then absorb and break down these particles. Artificial and natural wetlands are often used to treat stormwater and wastewater for this reason. And fifth, the combination of water and wildlife found in wetlands support several types of recreation, such as fishing, boating, hiking, and bird watching.
Unfortunately, wetlands are often threatened by human activities. Wetlands can either be completely eliminated or degraded so much so that their ecosystem cannot function. For example, wetlands are often drained to expose new land for agriculture or development or are flooded to create lakes. Over 96% of the original wetlands along western Lake Erie have been lost in this manner since the 1860s. In addition, runoff from lawns and impervious surfaces can add excessive amounts of pollutants such as fertilizers, pesticides, and sediment, which degrade the wetlands that absorb the material. A common land management technique is to build earthen dikes around wetlands, causing them to be hydraulically separated from surrounding areas. This artificial process eliminates the natural cycle of high and low water levels necessary for vegetation regulation. It also limits the movement of small biota in and out of wetlands, which is critical for the reproduction of many species.
Wetlands are also threatened by the spread of invasive species, also known as non-native, or exotic species. Both plants and animals can be considered invasive. These species are naturally very adaptable, and aggressive, and have a high reproductive capacity. They are considered invasive only when they spread outside of their natural range, where they out-compete native species due to their vigor and lack of natural enemies. Once established, they are extremely difficult to eliminate. Their presence in an ecosystem often causes economic, human health, and environmental damage. Some examples of invasive species in the Great Lakes Region are purple loosestrife, common reed, reed canary grass, narrow-leaved cattails, hybrid cattails (narrow/broad-leafed), emerald ash borer, common carp, sea lamprey, zebra mussels, and West Nile virus.
Recognizing the importance of wetlands is a relatively recent initiative. For example, the Ramsar Convention, an international treaty for the conservation of wetlands, wasn’t adopted until the mid-1970s. The U.S. North American Wetlands Conservation Act, which provides funding to protect and manage wetland habitat, wasn’t enacted until 1989. Since then, government agencies have created a set of laws regulating the use and management of wetlands. They also established a network of protected wetland areas that are managed by various state and federal agencies in which wetland managers try to restore degraded wetlands while attempting to balance the competing interests of recreation, habitat for particular species, and the spread of invasive species.
We are going to explore several of the data customization concepts described above in the context of a historical wetland restoration project within a federally protected area. The case study site is located in the Ottawa National Wildlife Refuge [2], located about 20 km east of Toledo, Ohio.