Continuous Instream Monitoring of Nutrients and Sediment in Agricultural Watersheds

Summary

With the advancement of technology and the rise in end-user expectations, the need and use of higher temporal resolution data for pollutant load estimation has increased. This protocol describes a method for continuous in situ water quality monitoring to obtain higher temporal resolution data for informed water resource management decisions.

Abstract

Pollutant concentrations and loads in watersheds vary considerably with time and space. Accurate and timely information on the magnitude of pollutants in water resources is a prerequisite for understanding the drivers of the pollutant loads and for making informed water resource management decisions. The commonly used "grab sampling" method provides the concentrations of pollutants at the time of sampling (i.e., a snapshot concentration) and may under- or overpredict the pollutant concentrations and loads. Continuous monitoring of nutrients and sediment has recently received more attention due to advances in computing, sensing technology, and storage devices. This protocol demonstrates the use of sensors, sondes, and instrumentation to continuously monitor in situ nitrate, ammonium, turbidity, pH, conductivity, temperature, and dissolved oxygen (DO) and to calculate the loads from two streams (ditches) in two agricultural watersheds. With the proper calibration, maintenance, and operation of sensors and sondes, good water quality data can be obtained by overcoming challenging conditions such as fouling and debris buildup. The method can also be used in watersheds of various sizes and characterized by agricultural, forested, and/or urban land.

Introduction

Water quality monitoring provides information on the concentrations of pollutants at different spatial scales, depending upon the size of the contributing area, which can range from a plot or a field to a watershed. This monitoring takes place over a period of time, such as a single event, a day, a season, or a year. The information garnered from monitoring water quality, mainly relating to nutrients (e.g., nitrogen and phosphorus) and sediment, can be used to: 1) understand hydrological processes and the transport and transformation of pollutants in streams, such as agricultural drainage ditches; 2) evaluate the efficiency of management practices applied to ....

Protocol

1. Site Selection

1. Watershed selection
   1. Select watershed(s) based on the magnitude of the pollution problem, priority of the watershed, proximity to the research facility, access to the site, and data objectives.
2. Stream sampling locations
   1. Select stream sampling location(s) based on the study purpose.
      NOTE: Optimal sampling locations are well-mixed within a cross-section, safely and easily accessible, geophysically stable (i.e., constant cross-section and a bank supportive of instrument station housing), and representative^12,

Results

In the Aryal and Reba (2017) publication, this protocol was used to study the transport and transformation of nutrients and sediment in two small agricultural watersheds⁶. Additional outcomes from this protocol are described below.

Rainfall-runoff Water Quality Relationships:

The strength of continuous monitoring is that users can choose a fine tim.......

Discussion

Overall, the continuous monitoring of nutrients and sediment has several advantages over monitoring using the grab sampling method. Hydrological and water quality processes are affected by rainfall over a very short span of time. Users can obtain high temporal-resolution data on nutrients and sediment to study complex problems. Other water quality parameters, such as conductivity, pH, temperature, and DO, can be obtained simultaneously and at the same cost as for monitoring nitrate, ammonium, and turbidity. Moreover, the.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Multiparameter sonde	Hach Hydrolab	DS5X	measures temperature, pH, conductivity, dissolved oxygen, nitrate, ammonium, turbidity
Area velocity flow module and sensor	Teledyne Isco	2150	measures average stream velocity and flow depth, and calculates flow rate and total flow based on provided cross-section area of the ditch. Stored data can be downloaded directly to computer.
Automatic portable water sampler	Teledyne Isco	ISCO 6712	automatically samples water in the set interval or in conjunction with flow module and sensor
Pressure Transducer	In-situ	Rugged Troll 100	measures presure, level and temperature in the water. Stored data can be directly downloaded to the computer
Portable flow meter	Flo-mate (Hach)	Marsh-McBirney 2000	For manual discharge measurement
Battery, 12 v, rechargeable	UPG	UB 1270	To power sonde
Battery, 12 v, rechargeable	Interstate Batteries	SRM 27	Lead acid battery to power autosampler
Solar panel	Alt E	ALT20-12P	To recharge battery at the site
C-8 batteries
Calibration standards	Hach or Fisher Scientific	mulitple	Standards of pH (4,7,10), conductivity (1412 uS/cm), nitrate (5 and 50 mg/L), ammonium (5 and 50 mg/L), and turbidity (50,100,200 NTU)
High nitrate standard	Hach	013810HY	50 mg/L
Low nitrate standard	Hach	013800HY	5 mg/L
High ammonium standard	Hach	002588HY	50 mg/L
Low ammonium standard	Hach	002587HY	5 mg/L
Turbidity standard	Fisher scientific	R8819050-500G	50 NTU
Turbidity standard	Fisher scientific	88-061-6	100 NTU
Turbidity standard	Fisher scientific	R8819200500 C	200 NTU
Potassium chloride salt pellets	Hach	005376HY	to maintain electrolyte for pH electrode
Potassium chloride standard	Fisher scientific	5890-16	1412 us/cm
Buffer solution, pH 4	Fisher scientific	SB99-1	for pH sensor calibration
Buffer solution, pH 7	Fisher scientific	SB108-1	for pH sensor calibration
Buffer solution, pH 10	Fisher scientific	SB116-1	for pH sensor calibration
Silicon sealant	Hach	00298HY	For sealing sensor battery cover water tight
All purpose cleaner	Sunshine Makers Inc	Simple green
Wipes	Kimberly-Clark
L-bracket
Telsbar post	Unistrut Service Company		Secure sensors and sondes in the stream
Steel wire			supend sonde and PT sensor
Carabiner			supend sonde and PT sensor
Allen wrench
Copper wire mesh	Bird B Gone		Rodent and bird control copper mesh roll
Adhesive Tape	Agri Drain Corporation		Tile tape, works in wet and cold weather