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5: Water Census

Anne B. Hoos, Gerard McMahon, and Michael D. Woodside

U.S. Geological Survey, Nashville, Tennessee

The SPARROW model (SPAtially-Referenced Regression on Watershed attributes) was used to investigate transport and fate of nitrogen on the landscape and in streams in river basins in Tennessee, North Carolina, South Carolina, Georgia, Alabama, Mississippi, and Florida. The SPARROW model integrates water-quality monitoring data with nitrogen source data to estimate mean-annual rates of combined overland and subsurface nitrogen transport from sources in a watershed to the adjacent stream channel. Delivery rates are characterized as functions of landscape factors such as soil permeability and depth.

The model produces estimates of mean annual load and concentration of nitrogen for each stream reach in the model area, providing a tool for addressing a number of questions about stream nitrogen loads entering nutrient-sensitive water bodies in the southeastern U.S. For example, what are the proportional contributions of nitrogen delivered to each water body from atmospheric deposition, agricultural land, urban land, and point-source wastewater discharge? How will changes in inputs from these sources affect the annual load delivered to the water body? SPARROW results can also address the proportional contributions of nitrogen to the water body from watershed subbasins, annual load responses to incremental changes in subbasin nitrogen inputs, and the effects of variation in landscape characteristics among subbasins.

Contact Information: Anne Hoos, U.S. Geological Survey, 640 Grassmere Park Drive, Nashville, TN 37211; phone: 615 837 4760; email: abhoos@usgs.gov

Leroy Pearman, U.S. Geological Survey, Florida Integrated Sciece Center, Orlando, Florida

The need for readily available water data has increased dramatically within the past 10 years. Data historically was disseminated using annual publications done on a National basis for each State. The States that rim the Gulf of Mexico all have viable data collection programs which collect continuous streamflow and water quality parameters in real-time. Stations exist on the major rivers and many of the smaller streams that enter the Gulf of Mexico. The discharges from month to month can vary by as many as three orders of magnitude which can cause major shifting in the saltwater-freshwater interface. The discussion will give the locations and types of data available throughout the TX, LA, MS, AL, and FL coastal areas. This data is invaluable in assessing the current and long-term changes occurring in the Gulf of Mexico.

Contact Information: Leroy Pearman, Florida Integrated Science Center, Orlando, FL 32826; phone: 407 803 5577;
email: jpearman@usgs.gov

Dennis K. Demcheck and Scott V. Mize

U.S. Geological Survey, Louisiana Water Science Center, Baton Rouge, Louisiana

The Bonnet Carre’ Spillway, located 28 miles above New Orleans, was constructed in the early 1930s as part of an integrated flood-control system for the lower Mississippi River system. Heavy rains in the Mississippi and Ohio River valleys in early spring 2008 increased the pressure on levees along the lower Mississippi River, threatening the City of New Orleans. In response, on April 11 the U.S. Army Corps of Engineers (COE) began opening the Spillway for the first time in eleven years. Mississippi River water was diverted into the 625-square mile Lake Pontchartrain, which retains a connection with the Gulf of Mexico. Average peak flows through the Spillway were about 169,000 cubic feet per second. The Spillway was closed on May 8.

On April 8 (3 days before the Spillway opening) the U.S. Geological Survey deployed a nitrate analyzer and a multi-parameter water-quality meter in Lake Pontchartrain at the request of the COE to assess the water-quality effects of the diversion on the Lake. The 2 units were suspended about 10 feet below the water surface (total depth 15 feet) at Lake Pontchartrain Causeway Crossover 7, about 15 miles east of the diversion and 3.5 miles from the south shore of the Lake. The units were programmed to record hourly measurements of nitrite + nitrate (presented as nitrate), water temperature, dissolved oxygen, specific conductance, salinity, and pH.

The nitrate analyzer operates using a standard “wet-chemistry” method of cadmium reduction/colorimetry: an alternative ion-selective probe that has been shown to perform poorly in high ionic-strength estuarine systems. The nitrate analyzer performs an automatic calibration with an internal standard every 12 hours and stores all waste reagents within the unit -- no toxic compounds are discharged into a receiving waterbody.

Both units recorded data hourly throughout the 27-day diversion. By May 23, the instruments had recorded the arrival, peak values, and decline of constituents associated with the freshwater influx from the Mississippi River/Bonnet Carre’ Spillway diversion. The value of hourly monitoring of nitrate concentrations and field parameters such as specific conductance is clearly illustrated during the period April 16-April 25. The data show the short-term interactions of high-nitrate, low specific conductance river water and low-nitrate, high specific conductance lake water. The maximum influence of river water at the site existed during April 26-April 30. The first indications of a gradual reversion to pre-existing lake conditions began on May 1.

Contact Information: Dennis Demcheck, U.S. Geological Survey, LA Water Science Center, Baton Rouge, LA ; phone: 225 298 5481; email: ddemchec@usgs.gov

Kenneth R. Odom, U.S. Geological Survey, Alabama Water Science Center, Montgomery, Alabama

Over recent years the term “water availability” has become very important as concerns grow about our ecosystem health, the effects of climate change, and the expanding population. But what really is water availability and how do we determine its present state? How do we predict future water availability?

Water availability is not only a question of water quantity, but also one of water quality. From a water quantity perspective, a hydroelectric power generation facility may be mainly concerned with the projection of monthly water volumes on a river system for predicting electrical power generation. Depending on other uses of the water, however, the quality can be as much a limiting factor as quantity. For example, the quantity of water available in an ecosystem for an endangered species may be ideal, but if some aspect of water quality is poor, the species’ survival may be in jeopardy.

Although water quality is essential to the determination of available water, the first step should be one of quantity. Indeed, if water is not available then how can water quality be measured in the first place? This presentation will focus more on the determination of water availability in terms of water quantity; however, this is not meant to downplay the importance of water quality but to provide a starting point for quantifying water resources.

Determination of water availability is usually multi-objective and multi-disciplinary, and requires a number of tools that can be modified, or customized, to site-specific conditions. No single method or model can be applied to all situations unless it is applied under broad-scale conditions. Determination of water availability, in general, requires expertise in a number of areas, including model building and calibration, statistics, geographical information systems, database design and management, and computer programming. Also, depending on the objectives of the water availability tool, one or more disciplines are required from geography, water, geology, and biology.

Successful determination of water availability is also time and space dependent. From the aspect of time, one particular study may require daily mean flows, while another study may require an annual water balance. Spatially, an ecosystem study may require water availability estimates at a stream-reach level while studies used for power generation and navigation may need quantity forecasts at a major river basin level.

Recent and ongoing water availability work in the Upper Flint River basin of Georgia is focusing on ecosystem flows. Coarse and fine resolution hydrologic models are being coupled with biological models to estimate the effects of changing water availability on fish populations at a stream reach level. Two hydrologic models are being used: TOPMODEL (TOPography-based MODEL) and PRMS (Precipitation-Runoff Modeling System). Both are physically-based models that can be customized to fit an array of scales in time and space. These are two tools that not only have the capability of simulating current conditions, but also are able to build scenarios for future predictions. TOPMODEL will also be used in a statewide water availability study in Alabama that will focus on daily mean flows at the spatial scale of 12-digit HUCs.

Contact Information: Kenneth Odom, U.S. Geological Survey, Alabama Water Science Center, AUM Techna Center,
Montgomery, AL 36117; phone: 334 395 4140 email: krodom@usgs.gov

Lisa E. Osterman1, Richard Z. Poore1, Peter W. Swarzenski2

1 U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida
2 U.S. Geological Survey, Pacific Science Center, Santa Cruz, California

Hypoxia occurs in continental-shelf subsurface waters when the uptake of oxygen by respiration exceeds its resupply. Systematic measurements of Louisiana continental-shelf waters were initiated in 1985, and since then hypoxia (oxygen content <2mg/L) has increased considerably in an area now dubbed the “dead zone.” Several monitoring and modeling studies have concluded that the expansion of the Louisiana shelf dead zone is related to increased nutrient delivery (primarily nitrogen, but possibly also phosphorous) from the Mississippi River drainage basin. The source of the nutrients is believed to be anthropogenic (fertilizer, sewage, and livestock-derived runoff, etc.) and is responsible for the degradation of Gulf of Mexico marine habitats. Our research investigates the record of temporal and geographic extent of low-oxygen bottom-water conditions recorded in Louisiana shelf sediment cores prior to 1985.

We use a specific low-oxygen faunal proxy termed the PEB index based on the cumulative percentage of three species of benthic foraminifers (= % Protononion atlanticum, + % Epistominella vitrea, + % Buliminella morgani) that has been shown statistically to represent the modern seasonal Louisiana hypoxia zone. Our hypothesis is that the increased relative abundance of PEB species in dated sediment cores accurately tracks the development and expansion of seasonal low-oxygen conditions on the Louisiana shelf. Fourteen box cores contain PEB records and excess 210Pb-derived chronologies. This network of core records reveals a consistent pattern showing the establishment of modern hypoxia over a large portion of the dead zone between 1950 and 1960. From 1960 to the present, the percentage of PEB species has steadily increased, indicating stronger or more frequent hypoxic episodes. These data also indicate that the occurrence of hypoxia hotspots, similar to those of today, existed much earlier on the shelf and as far back as 1920. Additional data support expansion of the modern dead zone to the south, where hypoxia has impacted the benthic foraminiferal faunas outside of the monitored area. Our results support the interpretation that modern hypoxia is related to human activities and subsurface low-oxygen conditions were occurring seasonally over at least two-thirds of the geographic distribution of the modern measured hypoxia zone by 1960.

Contact Information: Lisa E. Osterman, U.S. Geological Survey, Florida Integrated Science Center, 600 Fourth St. South, St. Petersburg, Florida 33701; phone: 727-803-8747 x 3084; fax: 727-803-2032; email: osterman@usgs.gov