Optimizing carbon to nitrogen ratios to improve nitrogen removal in agricultural drainage ditches

Transcription

1 Optimizing carbon to nitrogen ratios to improve nitrogen removal in agricultural drainage ditches Derek Faust, Robert Kröger, Leandro Miranda, Michael Cox, Matthew Moore, & Scott Rush Mississippi Water Resources Conference April 5, 2016

2 Source: LUMCON The Bigger Picture

3 Non-Point Nutrient Loading kg N H -1 yr -1 doubling in crop yield Agricultural sources 70% of N & P loads to Gulf of Mexico (Alexander, 2008) Nitrogen loads major cause of hypoxic zone (Daniel et al., 1994) 14,024 km 2 ( ) Size of Connecticut Goal: 5,000 km 2 Agriculture Urban NASA

4 Lower Mississippi Alluvial Valley

5 Agricultural Drainage Ditches

6 Drainage ditches may function like linear wetlands

7 BMPs in Drainage Ditches Larger ditches Two-stage ditches Vegetated ditches Slotted pipes Low-grade weirs

8 Denitrification NO 3 - NO 2- NO N 2 O N 2 Major limitations to denitrification: 1. Anaerobic soil conditions Low-grade weirs 2. Nitrate-Nitrogen 3. Organic carbon o Increased NO 3- -N removal with organic carbon amendments (Burchell et al., 2007). C:N ratios of 2.0 to 2.9 facilitated denitrification (Hamlin et al., 2008). C:N ratio of at least 20 necessary to meet needs of microbial decomposers (Sylvia et al., 2005)

9 Objectives 1. Evaluate how organic carbon amendments affect nitrate-nitrogen removal in agricultural drainage ditch systems 2. Determine effects of organic carbon amendments and flow rate on nitrate-nitrogen removal in a semi-controlled field setting using experimental drainage ditches 3. Assess relationships between organic carbon and nitrogen content of overlying water, pore water, and sediments of drainage ditches throughout the Lower Mississippi Alluvial Valley

10 Scale of Research Objective 1 Laboratory Objective 2 Experimental Ditches Objective 3 Field-LMAV

11 Effects of organic carbon amendments on nitrogen removal in agricultural drainage ditch sediments

12 Sub-objectives 1. Evaluate efficacy of dissolved (DOC) and particulate organic carbon amendments (POC) in nitrate-nitrogen removal after 3, 7, 14, and 28 days. 2. Quantify optimal carbon-to-nitrogen ratios for nitrogen removal with DOC and POC amendments.

13 Experiment 1 Design Control (No OC Amendment) DOC Amendment at 3.0 C:N POC Amendment at 3.0 C:N 3 days 7 days 14 days 28 days 3 days 7 days 14 days 28 days 3 days 7 days 14 days 28 days Overlying water (formulated moderately hard water) contained 3 mg L -1 NO 3 N 6 replicates per treatment

14 Experiment 2 Design Control (No OC Amendment) DOC Amendment C:N POC Amendment C:N Overlying water (formulated moderately hard water) contained 10 mg L -1 NO 3- -N 7 day time of incubation most optimal in experiment 1 6 replicates per treatment

15 DOC POC Control

16 Experiment 1 Nitrate Nitrogen Overlying Water

17 Experiment 2 Nitrate Nitrogen Overlying Water

18 Investigating organic carbon amendments with low-grade weirs as a best management practice for nitrogen removal in experimental agricultural drainage ditches

19 Objective Determine effects of organic carbon amendments and flow rate on nitrate-nitrogen removal in a semi-controlled field setting using experimental drainage ditches

20 Experimental Design NO N = 1 mg L -1 C:N = 5:1 Mixing Chamber Flow Rates Low Medium High Flow Legend Weir Inflow/ Outflow Pipe

21 Nitrate-nitrogen Concentrations

22 Understanding nitrogen and organic carbon contents of agricultural drainage ditches in the Lower Mississippi Alluvial Valley

23 Background 3.4% Organic Matter 1.7% Total Organic Carbon in sediment of drainage ditches (Littlejohn et al., 2014).

24 Objective Assess relationships between organic carbon and nitrogen content of overlying water, pore water, and sediments of drainage ditches throughout the Lower Mississippi Alluvial Valley.

25 Drainage Ditch Locations Sampled 89 drainage ditches 35 sites Criteria: Drained at least 10 ha of: Rice Soybeans Corn Cotton Bank full width 5 meters

26 Correlations Between Organic Carbon and Nitrogen 0.40 Sediment Percent N r = P < Sediment Percent TOC

27 Sediment Percent TOC Frequency Restored Wetlands 1.5 to 3.1% Natural Wetlands At least 10 to15% Sediment Percent TOC

28 Synthesis Organic carbon amendments increased NO 3- -N removal in laboratory 5:1 C:N ratio determined to be optimal NO 3- -N removal decreased by addition of flow to equation Drainage ditches are organic carbon limited Still some work to do to make organic carbon amendments a viable best management practice

29 Conclusions Where do we go from here? Try different organic carbon amendment techniques Slow release glucose (other simple saccharide) In-ditch bioreactor Hay weir

30 Conclusions In-ditch Bioreactor

31 Conclusions Hay Weir

32 Conclusions Where do we go from here? 1. Try different organic carbon amendment techniques Slow release glucose (other simple saccharide) In-ditch bioreactor Hay weir 2. Close the gap between lab experiments and ditches with flow 3. Monitoring of drainage ditches before and after organic carbon amendments

33 Acknowledgements MSU Water Quality Laboratory All those helping me locate sample sites Landowners and producers for generously providing permission to collect samples Funding Sources: Mississippi Agricultural and Forestry Experiment Station Forest & Wildlife Research Center WFA Faculty and staff Mississippi State University

34 Questions???