By Mary Waters, Texas Stream Team

Outline About the Arroyo Colorado

Basic information (geography) History Major uses

Water quality summary Segment 2202

Professionally collected data Volunteer collected data

Segment 2201 Professionally collected data Volunteer collected data

Watershed protection and TMDL

About the Arroyo Colorado

90 mile long water body with a watershed of 700 square-miles

Starts Southwest of Mission, TX and ends at the Laguna Madre

Upstream segment to Port Harlingen is freshwater, and downstream segment is tidal

Its source water is effluent from municipal wastewater-treatment plants, irrigation return flow, and storm water runoff, and base flows from shallow groundwater. During flooding, Rio Grande water can supply flows to the Arroyo Colorado

Arroyo Colorado Watershed and Major Stream Segments

History Before the turn of the

century, the natural stream meandered from the Rio Grande to the coast in a delta of thick semi-tropical forests and ending in a series of brackish wetlands

Land was cleared in the 1920’s and ‘30’s to make way for agriculture

Irrigation canals were built between 1900 and the early 1930’s.

The late 1940’s brought a large-scale flood control project to the entire Lower Rio Grande Valley

Major Uses

A floodway A conduit for

wastewater conveyance Irrigation source Recreational fishing and

boating Fish Consumption Commercial barge traffic Nursery for fish, shrimp

and crab Major source of

freshwater to the Laguna Madre

Habitat

Biodiversity

Neotropical migratory songbirds, snakes, lizards, fish and invertebrates

Mammals Ocelot Jagaurundi

Salamanders Black-spotted newt Lesser Rio Grande

siren

Water Quality

Water quality summary Segment 2202

Volunteer collected data

Professionally collected data

Causes of Water Quality Degredation Pollutant loading Degradation and

loss of aquatic and riparian habitat More than 95% of the

native brush land in the Lower Rio Grande Valley has been cleared for agriculture and urban development

Dredging for Barge Traffic

Professional Data

TCEQ’s Surface Water Quality Monitoring (SWQM) program.

The Nueces River Authority (NRA)

48 monitoring stations: 35 in Segment 2202 (non-tidal) 13 in Segment 2201 (tidal)

Volunteer Data

Professional Data Monitoring Sites

Segment 2202 (Headwaters to Port of Harlingen) Professional Data - Impairments

2202 Dissolved Oxygen and Water Temperature

Above Criteria Data (Professional) Dissolved Oxygen:

1 of 35 below criteria

Fecal Bacteria – 2202

E.Coli and Enterococcus Exceed the criteria

Segment 2201(Port of Harlingen to Laguna Madre) Professional Data - Impairments

Dissolved Oxygen - 2201

High Aquatic Life use designation

Associated 24- hour DO criterion: Average 4.0 mg/l minimum 3.0 mg/l.

Diurnal Variability: Low in the night and High in the afternoon

6 of 13 stations showed values below the criteria

Causes of Low Dissolved Oxygen in Segment 2201 nutrient loading

from the watershed

hydraulic effects in the dredged navigational channel

Nutrient Enrichment Problems Entire Arroyo Colorado Nitrogen exceed the

screening criteria from 1990 – 2006, increasing over time

Phosphorus concentrations exceed the screening criteria from 1990-2006, remaining the same over time

Chlorophyll-a, an indicator of excessive algal growth, exceed the screening criteria, reaching very high levels from 2000- 2006 (a similar trend to Nitrogen)

Fecal Bacteria

Figure 21. shows E. coli and Enterococcus

concentrations at water quality stations located

upstream (13074) and downstream (13072) of the

Tidal Segment boundary of the Arroyo Colorado from

2001 to 2006. E. coli concentrations in the Above Tidal

Segment of the Arroyo Colorado exceed the criteria

more frequently than in the Tidal Segment. The Above

Tidal Segment of the Arroyo Colorado is currently listed

on the 2004 Texas 303(d) list for elevated levels of E.

coli.

42 Fish Kills Documented 1976 -2004 Agriculture (7), Aquaculture (1) Industry (12) Municipal (5) Natural processes (8) Unknown (4) Weather (5) In 34 of the 42 events,

the direct cause of the fish kills was low dissolved oxygen in the water column

Most occurred in the tidal segment

Data Comparisons

Does the volunteer data show improvements or continued impairments?

Professional Volunteer

graph Table

Conclusions

Sources

QualityWater-Quality and Ancillary Data Collected From the Arroyo Colorado Near Rio Hondo, Texas, 2006

By Meghan C. Roussel, Michael G. Canova, William H. Asquith, and Richard L. Kiesling USGS

Handbook of Texas Online, Texas State Historical Association

A Watershed Protection Plan for the Arroyo Colorado – Phase I, 2007 (A Report of the Arroyo Colorado Watershed Partnership and Texas Sea Grant Pursuant to a 2003 USEPA Clean Water Act Section 319(h) Grant Awarded through Texas Commission on Environmental Quality Contract Agreement 583-4-65618)

Ocelot Image courtesy of tpwd.state.tx.us Spoonbill image courtesy of

lagunamadre.net