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Enhanced Access to Lakes Information
PEARL recently launched a series of new, easy-to-use, options for viewing water quality, biological and other information about Maine lakes. A series of buttons on the Lake Overview pages allows users to produce data summaries and graphics for any selected lake. Since these data displays are created “on-the-fly”, they always reflect the most up-to-date information in the PEARL Data Bank.
To access these lake information displays, first select a lake (PEARL Home > Data > Data Search: Lake / Stream Name). For example, entering Sebago Lake, will display the Lake Overview page for Maine’s deepest lake (Fig. 1).
Figure 1: Lake Overview page for Sebago Lake
The blue box in the Lake Overview provides morphometric and geographic information about the selected lake. Below the blue box is a series of buttons. When clicked, each of these buttons dynamically generates an extract of data from one or more of the tables in PEARL’s Data Bank. For example, the “Fish Species” button displays the list of Sebago Lake fish species as documented by the ME Dept. of Inland Fisheries & Wildlife (Fig. 2). To learn more about these fisheries data, the user can click on the metadata link above the table.
Figure 2. Segment of the Sebago Lake fish species list generated dynamically from the IF&W table in the PEARL Data Bank.
Other buttons on this Lake Overview page (Fig. 1) provide direct access to additional lake information, including water quality summaries, invasive plants, fish stocking and some invertebrate species lists. From this Lake Overview page, the PEARL user can also view dynamically generated graphs of water transparency (Secchi disk depth) and temperature / dissolved oxygen profiles (source data are provided by ME Dept. of Environmental Protection and the Volunteer Lake Monitoring Program). For example, clicking the Secchi Depth Plot button produces a graph of annual mean transparency data (Fig. 3a). To “drill down” into the transparency data for any year, simply click on the Secchi disk symbol; the within-year data are then displayed (Fig. 3b).
The Lake Overview pages also provide access to DEP’s Lake Narratives – short documents that provide a concise summary of water quality for the selected lake. For lakes with more than one distinct basin, these narratives are basin-specific (Station 1, 2, etc.) because different basins may exhibit different characteristics.
Figure 3a: Average annual Secchi disk transparency for Sebago Lake
Figure 3b: Secchi data for the year 2002
All of the data displayed via these buttons are lake-specific, “on-the-fly”, extracts from the source tables in PEARL’s Data Bank. To view the tabular source data for the selected lake, scroll down the Lake Overview page to view the icons depicting the “Available Data Categories”. Clicking on any of these icons reveals the suite of data tables that contain any records for the selected lake. Opening a table displays only those records for the selected lake. Users who wish to view (and possibly download) entire data tables (e.g. data for all sampled lakes) need to return to PEARL Home Page, select “Data” and then click on the button: “Browse all Titles in the PEARL Data Bank”.
Frequently-Asked Questions
Why are PEARL data divided into two broad groupings: “Lakes & Streams” and “Wetlands, Estuaries, Coastal & Terrestrial”?
The reason for this system of grouping data tables relates to the way in which PEARL data are spatially referenced. Lakes and streams data are referenced to individual waterbodies. All lakes data are identified by the MIDAS lake code (Moosehead Lake, for example, is 0390) – a system that was established by DEP and IF&W many years ago. Streams data are geo-referenced to individual stream segments using codes derived from the National Hydrographic Dataset (NHD: http://nhd.usgs.gov/). Internal lookup tables in the PEARL system link each MIDAS lake code or NHD stream segment to their landscape context: watershed (the series of nested hydrologic units developed by USGS: HUC-8, HUC-10 and HUC-12), town and county. These linkages allow PEARL users to search for data by watershed or by town/county, in addition to waterbody name or code.
In contrast to lakes and streams data, all other data types in PEARL are spatially referenced only by unique combinations of town and watershed (HUC-12). This spatial referencing system also allows the user to search for, and extract, data using either watershed or political boundaries.
Why are there more lakes and streams data in PEARL than wetlands, estuarine, coastal and terrestrial data?
This is simply a time issue. PEARL started about 8 years ago as an on-line forum for serving lakes data. Modifications to PEARL’s internal architecture that now enable other data types to be served on PEARL have been made only in the past 1-2 years. Now that these capabilities are in place, PEARL users will see an increasing number of both lake and non-lake data displayed on the site.
For questions, comments or more information about PEARL, contact PEARL@maine.edu.
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