Beneath the Surface

Decoding Indiana's River Sediments and What They Reveal

The Hidden World Underwater

Imagine Indiana's rivers as living history books. The muddy bottoms—where pollutants settle—hold secrets about industrial pasts, agricultural runoff, and ecological resilience. The National Sediment Inventory (NSI), managed by the EPA, is a massive database tracking contaminants in U.S. waterways since the 1980s. In Indiana, this intersects with ecoregions—unique environmental zones shaping how toxins accumulate 1 .

River sediment

Sediment cores reveal layers of environmental history in Indiana's waterways.

Why Sediment Matters

Sediment isn't just dirt—it's a sponge for pollutants. Heavy metals, pesticides, and industrial chemicals bind to particles, accumulating over decades. When stirred by floods or dredging, these toxins re-enter water, threatening aquatic life and human health.

Key Concepts:

The EPA's BASINS System

Integrates water quality data, hydrology, and climate. The NSI within BASINS includes:

  • Sediment chemistry (contaminant concentrations)
  • Tissue residue (toxins in organisms)
  • Toxicity tests (biological impacts) 1
Ecoregions in Indiana

Divided into 6 Level III zones, each with distinct geology and land use affecting sediment contamination:

  • Central Corn Belt Plains: High agricultural runoff.
  • Driftless Area: Less industrial impact.
  • Wabash/Ohio River Valleys: Industrial hotspots .

Case Study: The Wabash River Sediment Survey

How scientists measure hidden pollution.

Methodology:

  1. Site Selection: 20 stations across Indiana's Wabash ecoregion (Level IV #54), targeting industrial and agricultural zones.
  2. Sampling: Sediment cores extracted with piston corers—layers dated to track contamination timelines.
  3. Triad Assessment:
    • Chemistry: Tested for PCBs, mercury, arsenic.
    • Toxicity: Exposed amphipods (Hyalella azteca) to sediment.
    • Tissue Analysis: Measured toxins in resident mussels 1 .

Results & Analysis:

Table 1: Contaminant Levels in Wabash Sediments
Contaminant Avg Concentration (ppm) EPA Threshold Exceedance (%)
PCBs 0.18 0.05 85%
Mercury 0.32 0.15 70%
Arsenic 9.1 8.2 45%

Amphipod survival dropped by 65% at PCB-hotspots, confirming ecological harm. Mussels showed mercury levels unsafe for human consumption.

Indiana's Sediment Hotspots: An Ecoregion Lens

Table 2: Contaminant Trends by Ecoregion
Ecoregion (Level III) Dominant Contaminants Key Sources Toxicity (%)
Central Corn Belt Plains Atrazine, Nitrates Agricultural runoff 25%
Southern Michigan/Driftless Low contaminants Forested buffers 5%
Interior River Valleys PCBs, Mercury Industrial discharge 60%

Data from EPA BASINS 3.0 shows 40% of Indiana's industrial zones exceed sediment safety benchmarks 1 .

The Scientist's Toolkit: Sediment Analysis Essentials

Table 3: Key Field & Lab Tools
Tool/Reagent Function Indiana Application
Piston Corer Extracts intact sediment cores Preserves layer history in Wabash
Gas Chromatograph Detects organic pollutants (PCBs, pesticides) ID's agricultural toxins statewide
Hyalella azteca Toxicity test organism Measures biological impact in labs
Ecoregion GIS Maps Guides targeted sampling Prioritizes high-risk zones
Piston Corer
Chromatograph
Amphipods
GIS Maps

Why This Work Changes Indiana's Future

Sediment data shapes cleanup priorities. Fort Wayne's Riverside Park used NSI data to secure Superfund status in 2023. The EPA's ecoregion framework helps tailor solutions: wetlands for farm runoff, dredging for industrial zones .

"Sediments tell stories water can't."

Dr. Lena Rossi, Indiana EPA Hydrologist
Your Role

Support local sediment monitoring—report pollution spills and join watershed groups. Indiana's rivers depend on it.

Explore NSI Data Download Ecoregion Maps

References