NoVA Wetland Conservation Priority Atlas

OverviewA Priority List, Not Another Choropleth

This is a synthesis dataset. It joins the Day 53 Wetland Development Pressure Atlas (2,781 NLCD-derived wetland complexes, each scored by surrounding imperviousness) to the Day 58 Protected Lands and Conservation Easement Atlas (PAD-US 4.1 fee tracts and easements), to answer a question neither can answer alone: of Northern Virginia's wetlands, which are simultaneously under development pressure, not yet protected, and close enough to the existing conservation network that acquiring them would consolidate a corridor rather than create an island.

Of 2,781 wetland complexes, only 684 (24.6 percent) have a majority of their area inside the protected-lands footprint. High-pressure wetlands are protected at 23.2 percent - statistically no safer than average. The Wetland Conservation Priority Index (WCPI) ranks the 1,377 unprotected High- and Moderate-pressure complexes; 138 rank Critical, and 28 DBSCAN acquisition target zones consolidate the highest-priority sites.

Why This DatasetThe Gap Between Pressure and Protection

Land trusts and county open-space programs work with finite acquisition budgets. The hard question is not 'where are the wetlands' (NWI answers that) or 'what is protected' (PAD-US answers that) - it is where does unmet need concentrate. A wetland already inside a park needs no action; a wetland under an approved subdivision is already lost; the acquisition sweet spot is the pressured-but-savable middle, ideally next to land a trust already holds so stewardship is cheap and the corridor grows. That intersection is exactly what falls between Day 53 and Day 58, and it is what this atlas isolates and ranks.

MethodologyHow the Priority Index Was Built

Both parent layers were reprojected to EPSG:32618 and repaired with a zero-width buffer. Each wetland complex was classified as protected (>=50% of its area inside the in-region PAD-US 4.1 footprint), partly protected (5-50%), or unprotected by intersection area.

Per the program's verification gate, demand (wetlands) is clipped to the 9 NoVA jurisdictions but supply (protected land) is not: distance to the nearest protected unit is measured against a 12 km-buffered USGS PAD-US GAP-status ring of 4,254 units, so a wetland near the western Loudoun or southern Prince William boundary is measured against protected land just outside the region. 322 of 2,097 unprotected complexes are in fact nearer to out-of-region protected land.

Components are min-max normalized to 0-1 and equally weighted. Priority tiers are WCPI quartiles: Critical (>=90th percentile), High (75-90), Moderate (50-75), Watch (<50). Haversine DBSCAN (eps=1,200 m, min_samples=5) on the top-half-priority complexes delineated 28 acquisition target zones (283 isolated).

Key FindingsWhat the Data Shows

• Only a quarter of NoVA wetlands are protected. 684 of 2,781 complexes (24.6%); high-pressure wetlands fare no better (23.2%).
• Prince William County carries the largest gap - 650 candidates (8,107 acres), 71 Critical, and just 15.7% of its complexes protected.
• Fairfax County has already done the protecting (45.1%, triple Loudoun's 12.5%), so its 338 remaining candidates are the region's most defensible 'finish the job' targets.
• Top site: a 316-acre unprotected emergent wetland in Prince William County (complex #2152) abutting an existing easement under 37.7% imperviousness - WCPI 0.76.
• 28 acquisition target zones. The largest - 67 complexes / 980 acres in southern Prince William (26 Critical) and an 841-acre Fairfax cluster (14 Critical) - are corridor-scale, not one-off parcels.

Analytical UsesWhat You Can Do With This

• Land-trust acquisition pipelines. A defensible, reproducible first-cut of where limited dollars protect the most at-risk wetland acreage - for NVCT, VOF, and county open-space programs.
• Mitigation banking siting. High-WCPI clusters flag where compensatory-mitigation demand and supply co-locate - the precondition for a viable wetland bank.
• Comprehensive-plan open-space targets. Jurisdictions can weigh their protection rate against their pressure exposure to set numeric goals.
• Chesapeake Bay / 303(d) screening. Overlay the Critical tier with the Day 42 Impaired Waters Atlas to find unprotected wetlands whose loss would most degrade already-impaired downstream segments.

Synthesis OpportunitiesWhat It Combines With

Intersect the Critical tier with the Day 42 Impaired Waters Atlas to prioritize wetlands draining to sediment- or temperature-impaired segments. Join to the Day 39 Traffic Volume Atlas to add a chloride/hydrocarbon road-runoff dimension to high-pressure clusters near major corridors. Cross the acquisition zones with the Day 30 Income Inequality Atlas to test whether conservation investment is being sited equitably. And pair with county building-permit feeds to measure the lag between permit issuance and observable wetland-buffer clearing.

LimitationsKnown Caveats

• Wetland extent is NLCD-derived, not NWI or field-delineated; small and narrow riparian wetlands are under-captured and boundaries are 30 m-raster generalized.
• Protection status is a snapshot. PAD-US 4.1 lags recent easements and pending deals; establishment year is present for only ~41% of Day 58 units, so no temporal trajectory is modeled.
• Corridor closeness uses in-region easements only - the network an acquisition would extend. Out-of-region and fee-owned protected land inform the separate protection-distance field, not the index.
• The index ranks, it does not appraise. WCPI reflects pressure, size, and corridor value - not land cost, owner willingness, hydrologic function, or developability. It is a screening tool for field follow-up.
• Falls Church City and Manassas Park City have negligible wetland bases (1 and 2 complexes); their statistics are not comparable to the counties.

Data DictionaryFields in the GeoPackage

Jurisdiction BreakdownResults by Jurisdiction

Sources & CitationsAll Data is Openly Licensed

• [1]U.S. Geological Survey. Protected Areas Database of the United States (PAD-US) 4.1, Protection Status by GAP Status Code. USGS Gap Analysis Project. Retrieved 2026-07-14.
• [2]Keystone GIS. NoVA Wetland Development Pressure Atlas (Day 53). NLCD 2021 wetland complexes with 250 m imperviousness pressure tiers. DOI 10.5281/zenodo.21251778.
• [3]Keystone GIS. NoVA Protected Lands and Conservation Easement Atlas (Day 58). Deduplicated PAD-US 4.1 fee tracts and easements. DOI 10.5281/zenodo.21321233.
• [4]Multi-Resolution Land Characteristics Consortium. National Land Cover Database (NLCD) 2021.
• [5]U.S. Census Bureau. 2023 Cartographic Boundary Files, Counties (1:500,000).