Aquatic Core Networks, Northeast U.S.

The aquatic core networks is one of a suite of products from the Nature’s Network project (naturesnetwork.org).

These datasets represent the aquatic core networks, which include lotic and lentic core areas and aquatic buffers. NOTE - The aquatic buffers dataset has been converted to integers and only contain values of 90 -100 (0.9 - 1) for online purposes, the original dataset is included in the download and contains all values. All datasets in this map are included in the download.

The aquatic core networks represents intact, well-connected stream reaches, lakes, and ponds in the Northeast and Mid-Atlantic region that, if protected as part of stream networks and watersheds, will continue to support a broad diversity of aquatic species and the ecosystems on which they depend. The cores include especially intact, resilient examples of each major aquatic ecological system across the region along with habitat for priority aquatic species. The core network offers guidance for conserving aquatic biodiversity and ecological function into the future by providing tools to help identify, prioritize, protect, and effectively manage the full range of aquatic systems in the region along with representative and priority fish and wildlife species.

The aquatic core networks are comprised of three datasets: lotic (river and stream) cores, lentic (lake and pond) cores, and the aquatic buffers. The lotic cores and lentic cores represent the most intact examples of each aquatic habitat class based on UMass’ Index of Ecological Integrity (IEI). IEI assesses 21 stream classes based on gradient, temperature, and size (lotic) and 12 lake/pond classes based on temperature, depth, and trophic class (lentic). The cores also represent habitat for representative priority aquatic species using a range of these habitat types across the region. These include headwater streams with the highest probability of occurrence for Eastern brook trout, and known rivers and streams supporting Atlantic and shortnose sturgeon, salter brook trout, the highest priority watersheds for alewife, American shad, and blueback herring, and priority rearing habitat for Atlantic salmon in the Gulf of Maine watershed. Lentic cores also include lakes and ponds with the highest habitat suitability for common loon. Aquatic buffers surround the aquatic (both lotic and lentic) cores. Buffers represent the areas estimated to have a strong influence on the integrity of the aquatic cores based on watershed processes. They include the areas that are hydrologically connected to the cores, based on the idea that human actions (such as development or pollution) within the buffer area may impact the integrity of the aquatic cores. As a result, the land underlying the buffers is not necessarily of high ecological integrity.

Intended Uses

• Determine where to start protection and management for a range of intact aquatic systems

• Identify areas and networks of high ecological value

• Pinpoint important areas for aquatic core buffers

• Restore connectivity to otherwise intact areas

The aquatic core and buffer network can serve as a starting point for a regional conservation network that can be used in combination with other sources of information to direct action. Suggestions include:

Lotic and lentic cores can serve as a starting point for a regional conservation network that can be used in combination with other sources of information to direct action. Suggestions include:

• Use in combination with other data layers to identify additional areas of high ecological value. Layers to consider include: 1) the terrestrial core-connector network, 2) The Nature Conservancy’s (TNC) Freshwater Resilience Networks, 3) the aquatic Index of Ecological Integrity, 4) habitat maps for Common Loon and important fish species (brook trout, Atlantic salmon, and other anadromous species), and 5) habitat condition for imperiled species.

• Use in conjunction with aquatic connectivity restoration priorities to identify areas where restoring connectivity will add value to areas that are already intact.

• Use in combination with the secured lands layer to identify aquatic core areas and buffers that remain unsecured from development, and thus could represent priorities for protection.

• Use in combination with the probability of development layer and regional vulnerability layers to identify places in the aquatic core area network that are relatively vulnerable to future development, and thus could represent priorities for protection.

• Identify overlap between this network and resource priorities identified at the state or local level, but that are not available across the entire region (e.g., from State Wildlife Action Plans, towns, and land trusts), to further rank areas for protection.

Description and Derivation

The aquatic core network is based on a set of regional analyses that assess the physical and biological value of aquatic systems and species across the Northeast region. The core area network integrate five components

1. The most integral locations of each of 21 stream habitat classes and 12 lake/pond habitat classes in HUC 6 watersheds across the Northeast. Ecological systems were mapped by the Nature Conservancy working with the Northeast state fish and wildlife agencies and the North Atlantic LCC. Their integrity has been assessed using the Index of Ecological Integrity developed by the University of Massachusetts Amherst with the North Atlantic LCC.

2. Lotic core areas representing the highest probability of occurrence for Eastern brook trout (rep. species for cold headwater streams) not captured by lotic ecosystem cores.

3. Lentic cores representing the highest landscape capability for common loon (representative species for intact lakes and ponds) not captured by lentic ecosystem core.

4. Stream reaches with a) existing occurrences for Atlantic and shortnose sturgeon, and salter brook trout, b) the  top 5% of watersheds for alewife, American shad and blueback herring (data from Trout Unlimited) and c) priority rearing habitat for Atlantic salmon in the Gulf of Maine (from U.S. Fish and Wildlife Service), where not already captured in cores.

5. Aquatic core area buffers based on areas in the upstream watershed most likely to influence the core areas.

This version of aquatic core areas is based on stratifying the ecosystem input, the Aquatic Index of Ecological Integrity, by large watershed (HUC 6 level). This ensures that core areas are well-distributed across the landscape. However, in this stratified version, the core areas do not comprise 30% of each watershed. Once the core "seeds" were determined, the entire corresponding lake or pond was deemed a lentic core, and the lotic cores were grown out giving priority to long continuous high-quality areas, rather than alligning with watershed boundaries. This stratification also means that some of the highest quality examples of ecosystems and habitats from a regional perspective are not included in core areas, where their inclusion would otherwise result in more than 30% of the aquascape in the region. A complementary version of aquatic core areas that is not stratified by watershed is also available as part of the Nature’s Network package.

These core areas and buffers are intended to be overlain with additional analyses including Freshwater Resilience Highest and High watersheds developed by The Nature Conservancy and the version of regionally scaled, unstratified aquatic core areas.

Attribute Information and Field Definitions

Lotic Cores:

• FID = ESRI assigned unique number (which we do not use) for each polyline.
   

• Shape = ESRI assigned feature geometry, type = "polyline".
   

• coreID = unique number (ID) assigned to the core.
   

• lengthKm = stream length (km) of the core. The length of the lotic core is approximated by the number of 30 m centerline cells. In addition, lotic cores can include centerlines through contiguous wetlands as well as contiguous lentic cores; thus, length of the lotic core represents the approximate length of contiguous lotic (including through wetlands) and lentic cores.
   

• system1, system2, system3 = list of the top three lotic ecological systems for which the core is particularly important; specifically, systems for which the cumulative ecological integrity of the system within the core is greater than expected (from a statistical perspective) given its distribution across the entire core area network. Note, the lotic systems listed here are not necessarily the most abundant systems in the core, but rather reflect the systems for which the core is especially important.

• troutSum = sum of the brook trout probability of occurrence index in the core.
   

• troutMean = mean of the brook trout probability of occurrence index in the core.

• salmonSum = total number of cells in the core comprised of the top 10% of Atlantic salmon rearing habitat.
   

• salmonMean = percentage of the core comprised of the top 10% of Atlantic salmon rearing habitat.
   

• anadSum = total number of cells in the core comprised of the designated anadromous fish habitat, including all sturgeon and salter brook trout rivers and streams, and the top 5% HUC12 watersheds for the three Alosid species.
   

• anadMean = percentage of the core comprised of the designated anadromous fish habitat.
   

• ecoURL = contains links to the Ecosystem tables for each core area. Ecosystem tables contain a complete listing of all aquatic systems present in the core (including wetland and lentic systems), along with their relative abundance. See the technical documentation for more information (http://jamba.provost.ads.umass.edu/web/lcc/DSL_documentation_aCores.pdf).

Lentic Cores:

• FID = ESRI assigned unique number (which we do not use) for each polygon.
   

• Shape = ESRI assigned feature geometry, type = "polygon".
   

• coreID = unique number (ID) assigned to the core.

• areaHA = area of the core in hectares.

• System = The ecosystem type of the core

• loonSum = sum of the loon landscape capability index in the core

• loonMean = mean of the loon landscape capability index in the core

• ecoURL = contains links to the Ecosystem tables for each core area. Ecosystem tables contain a complete listing of all aquatic systems present in the core (including wetland and lentic systems), along with their relative abundance. See the technical documentation for more information (http://jamba.provost.ads.umass.edu/web/lcc/DSL_documentation_aCores.pdf).

Aquatic Buffers:

• Value = the magnitude of influence based on the time-of-flow model; values range from 1 (maximum influence) at the core to zero 0 (no influence) at the cell with the least influence (i.e., furthest upstream and upslope of the core).

Known Issues and Uncertainties

As with any project carried out across such a large area, aquatic core networks are subject to limitations. The results by themselves are not a prescription for on-the-ground action; users are encouraged to verify, with field visits and site-specific knowledge, the value of any areas identified in the project. Known issues and uncertainties include the following:

• The classification and mapping of aquatic ecological systems is known to be imperfect, which consequently affects the mapped values for ecosystem integrity and species habitat. While the ecosystem mapping is anticipated to correctly reflect broad patterns of ecosystem occurrence, errors in classification and placement do occur, as with any regional GIS data. In addition, errors in mapping and alignment of hydrography, development, roads, traffic rates, and a number of other data layers can affect the model results.

• It is not possible to map all factors affecting ecological integrity and species habitat across the Northeast, and the omission of such factors can be anticipated to pose some limitations in the results. Examples are listed below.

  • The aquatic core network does not currently account for flow impairment as this information is only available at the medium resolution (1:100k) hydrography.

  • The aquatic core network does not include information on non-indigenous aquatic species, or instream habitat quality because the available data are too coarse (HUC 8 watersheds) for the region.

  • Core areas do not account for instream habitat quality because there are no consistent data across the region; partners can incorporate local or state data if available.

• The core area network approach by design does not explicitly identify the most important areas for rare aquatic species; however some additional areas are covered with the Habitat for Imperiled Species component and should be used as a complementary dataset.