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