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Wet and Dry Deposition Study: Texas Coastal Bend Bays and Estuaries Program (CBBEP)
Terry L. Wade*, Stephen T. Sweet
Geochemical and Environmental Research Group (GERG), Texas A&M University
833 Graham Rd., College Station, TX 77845
Clyde W. Sweet (retired)
Illinois State Water Survey, 2204 Griffith Dr., Champaign, IL 61820
| Atmospheric deposition studies were instituted
at two sampling sites on Corpus Christi Bay, Texas in 1997 as part of
CBBEP. In 2002 the Texas A&M University, Corpus Christi (TAMUCC) site
became an official NADP site (TX 39), the first located in close proximity
to an urban/industrialized/estuarine area. The flux of inorganic nitrogen
via atmospheric deposition was estimated from data collection that began
in the late spring of 1997 and continued through September 1999 at the
two sampling sites. Wet only rain samples were collected with an AeroChemetric
rain sampler. Dry deposition (1997 to 1999) was estimated from analytes
deposited to “clean water” in the dry side bucket of the AeroChemetric
rain sampler. This study was the first attempt to characterize atmospheric
loading rates of nitrogen in both wet and dry deposition to the Coastal
Bend Bays estuaries. Dry deposition is dominated by ammonium at both the
Texas A&M University Corpus Christi Station (TAMUCC) and at Whites
Point Station (WP). Wet deposition of nitrogen directly to the coastal
bend bays and estuaries ranges from 3.6 to 4.4 x 105 kg and dry deposition
ranges from 5.6 to 7.6 x 105 kg based on rates from these two stations.
The wet depositional rate of nitrate and ammonium at TAMUCC and at WP
for 1998 was 1.15 and 1.36 kg N/ha-yr; 1.60 and 1.50 kg N/ha-yr, respectively.
Wet deposition rates of nitrate at the two sites in Corpus Christi are
similar to the NADP/NTN site located in Beeville, Texas (1.2 kg N ha-1
yr -1) and at the TAMUCC NADP (TX 39) in latter years; however, the ammonium
flux is higher at Beeville,TX (2.0 kg N/ha-yr) for 1998. The dry depositional
rate of nitrate and ammonium at TAMUCC and at WP for 1998 was 0.91 and
4.41 kg N/ha-yr, 1.31 and 2.60 kg N/ha-yr, respectively. Coupled studies
(n = 8) of dry deposition to an empty AeroChemetric rain sampler bucket
compared to one with clean water indicated similar collection efficiency
for nitrate, but enhanced efficiency for ammonium. Based on these studies
it is likely that NADP wet only nitrogen deposition for Costal Bends Estuaries
underestimates, by over a factor of 2, the actual nitrogen deposition.
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