Temporal variations and scaling of streamflow and baseflow and their nitrate-nitrogen concentrations and loads

doi:10.1016/j.advwatres.2004.12.014

Advances in Water Resources

Volume 28, Issue 7, July 2005, Pages 701-710

https://doi.org/10.1016/j.advwatres.2004.12.014 Get rights and content

Abstract

The patterns of temporal variations of precipitation (P), streamflow (SF) and baseflow (BF) as well as their nitrate-nitrogen (nitrate) concentrations (C) and loads (L) from a long-term record (28 years) in the Raccoon River, Iowa, were analyzed using variogram and spectral analyses. The daily P is random but scaling may exist in the daily SF and BF with a possible break point in the scaling at about 18 days and 45 days, respectively. The nitrate concentrations and loads are shown to have a half-year cycle while daily P, SF, and BF have a one-year cycle. Furthermore, there may be a low-frequency cycle of 6–8 years in C. The power spectra of C and L in both SF and BF exhibit fractal 1/f scaling with two characteristic frequencies of half-year and one-year, and are fitted well with the spectrum of the gamma distribution. The nitrate input to SF and BF at the Raccoon watershed seems likely to be a white noise process superimposed on another process with a half-year and one-year cycle.

Introduction

Excessive nitrate-nitrogen (nitrate) concentrations and loads in surface waters present a myriad of water quality impairments to downstream receptors. Nitrate concentrations that exceed the maximum contaminant level of 10 mg/l threaten public water suppliers that use surface water intakes. Export of nitrate loads from the Midwestern agricultural region of the United States has been identified as a major contributor to hypoxic conditions in the Gulf of Mexico [6], [15], [30]. Nutrient enrichment and eutrophication are further linked to excessive loss of nitrate into surface water [11], [44], [46], [48]. Reduction of nitrate in streams and rivers is becoming increasingly important. For example, policies developed under the U.S. Clean Water Act of 1972, Section 303(d) seek to determine the total maximum daily load (TMDL) a water body can assimilate without impairment of beneficial uses. Therefore, understanding the dynamics of both water flow and nitrate concentrations is critical if TMDL control strategies are to be provided that reduce nutrient fluxes from agricultural regions.

Streamflow and nitrate concentrations and loads vary over time due to differences in biogeochemical processes and land management in watersheds [42]. Over decadal time scales, streamflow conditions and nitrate concentrations have changed in many Midwestern rivers. Increasing nitrate concentrations have been observed in stream waters over the last 50 years [41]. A two- and threefold increase in nitrate concentrations has been observed in the Cedar and Des Moines Rivers in Iowa during the period of 1940–2000 [18]. During the second half of the 20th century, stream gauging records have documented changes in hydrology that have resulted from improved land conservation and changing land management practices in the agricultural Midwest [13], [28], [34]. Over shorter daily, seasonal, and annual time scales, streamflow conditions and nitrate concentrations and loads are known to vary considerably. Many investigators have described variable nutrient fluxes in agricultural watersheds [2], [3], [6], [10], [27], [32]. Transport of nitrate has been shown to vary markedly with season [1], [19], [26], [27], [35] and vary due to geologic controls on groundwater discharge [38] and land use differences [12], [26], [27], [33], [36]. Inputs from storm events further accentuate intermittent loading of nonpoint source pollutants [8], [27].

To gain better understanding of the dynamics of nutrient fluxes, time-series analysis has been carried out with long-term streamflow and chemical concentration records [4], [7], [21], [24], [37], [47], [49], [50]. Detailed time series analysis of autoregressive modeling of river nitrate concentrations was used by Worrall and Burt [49] to show a memory effect in the time series. Worrall et al. [50] described the memory effect as a “form of persistence, with the previous condition of nitrate export in the catchment influencing present nitrate export”. The “memory” contained in time-series records was evaluated using spectral analysis by Kirchner et al. [21] in relation to chloride concentration in rainfall and runoff from a headwater catchment in Wales. Chloride concentrations were found to exhibit white noise spectrum in rainfall but fractal 1/f scaling in streamflow over three orders of magnitude [21]. The fractal scaling found in stream chloride concentrations implied that chloride concentrations in streams would be sustained for a long period of time, in essence containing a memory of past inputs.

The purpose of this study is to analyze a long-term (28 years) record of streamflow and nitrate concentrations and loads for the Raccoon River, Iowa to evaluate temporal variations and determine whether temporal scaling exists in these important variables. Unlike chloride, nitrate is highly reactive with many natural and artificial sources that vary spatially and temporally in an agricultural watershed. Moreover, in Midwestern agricultural watersheds, nitrate is primarily delivered to streams through groundwater discharge and tile drainage [16], [33]. Herein, consideration is given to temporal scaling in nitrate concentrations and loads in both streamflow and baseflow transport in the Raccoon River. Detecting whether temporal scaling exists in these processes will provide better understanding of the dynamics of nitrate fluxes from agricultural systems. This understanding is essential for developing effective strategies to reduce nitrate in stream waters for protection of water supplies and sensitive watershed ecosystems.

Section snippets

Description of the study area and data

The Raccoon River is a tributary of the Des Moines River that flows to the Mississippi River (Fig. 1). It drains a watershed of 8908 km² above the City of Van Meter in west-central Iowa. The North, Middle and South Raccoon rivers form major tributary branches to the Raccoon River. The North and Middle Raccoon Rivers flow through the recently glaciated Des Moines Lobe landform region of Iowa, a region dominated by low relief and poor surface drainage [29]. The South Raccoon river drains an older

Temporal variations of streamflow and baseflow and their nitrate concentrations and loads

Daily precipitation (P) and streamflow (SF) in the Raccoon River fluctuated and exhibited a wide range of values (Fig. 2a and b). The annual mean P was 870 mm and the annual maximum daily SF was often larger than 250 m³/s, with occasional events exceeding 850 m³/s, whereas minimum flows were typically less than 0.3 m³/s. Nitrate concentrations (C) ranged from less than 0.05 mg/l in 1977 in several occasions to 17.0 mg/l in 1982 and 1990 (Fig. 2c). Of the 981 weekly and bimonthly collected samples for

Temporal scaling of streamflow, baseflow, and nitrate concentrations and loads

The patterns of temporal variations of P, SF, BF, and C and L in SF and BF are also analyzed with spectral analysis. The spectra of the daily P and SF are calculated with the SPECTRUM function in MATLAB but that of BF are estimated using the computer code REDFIT v. 3.5 [40] since the data samples were collected at unevenly-spaced time intervals. REDFIT estimates the spectrum by fitting a first-order autoregressive process directly to an unevenly spaced time series. It is seen that the spectrum

Watershed travel time distribution and nitrate sources

Scaling in the observed nitrate concentrations in SF and BF at the Raccoon River indicate persistence or memory effect of past inputs. This effect may be quantified by the watershed’s travel time distribution [21]. Based on the observed fractal fluctuations in the chloride concentrations in streamflow at Hafren, Wales, Kirchner et al. [21] found that the watershed travel time may be described with the approximate power function of the gamma distribution, $y (t) = \frac{t^{α - 1}}{λ^{α} Γ (α)} e^{- t / λ}$ where t is time and Γ

Conclusions

1.
The nitrate concentration (C) and load (L) have a half-year cycle while daily precipitation (P), streamflow (SF) and baseflow (BF) are known to have a one-year

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Temporal variations and scaling of streamflow and baseflow and their nitrate-nitrogen concentrations and loads

Abstract

Introduction

Section snippets

Description of the study area and data

Temporal variations of streamflow and baseflow and their nitrate concentrations and loads

Temporal scaling of streamflow, baseflow, and nitrate concentrations and loads

Watershed travel time distribution and nitrate sources

Conclusions

J Hydrol

J Hydrol

J Hydrol

J Hydrol

Comput Geosci

J Hydrol

Seasonal runoff losses of nitrogen and phosphorus from Missouri valley loess watersheds

J Environ Qual

Streamflow induced variations in nitrate flux in tributaries to the Atlantic coastal zone

Biogeochemistry

Effect of stream channel size on the delivery of nitrogen to the Gulf of Mexico

Nature

Agricultural-nitrogen contributions to hypoxia in the Gulf of Mexico

J Environ Qual

Stream nitrate levels in a small catchment in southwest England over a period of 15 years

Hydrol Process

Nonpoint pollution of surface waters with phosphorus and nitrogen

Ecol Appl

Numerical analysis for the geological sciences

Anthropogenic inputs of nitrogen and phosphorus and riverine export for Illinois, USA

J Environ Qual

Establishing nutrient criteria in streams

J North Am Benthol Soc

Streamflow trends in Wisconsin’s driftless area

Water Res Bull

Stochastic subsurface hydrology

Nitrates in ground water in Iowa

Water quality in Walnut Creek watershed: herbicides and nitrate in surface waters

J Environ Qual

Mining geostatistics