Ecosystem structure and function in two branches of an eastern Minnesota, USA, trout stream

Figures & data

Figure 1. Map of Valley Creek, MN, USA showing study locations. This map was created using ArcGIS software by Esri. ArcGIS and ArcMap™ are the intellectual property of Esri and are used herein under license. Copyright © Esri. All rights reserved. For more information about Esri software, please visit www.esri.com.

Table 1. Physical and chemical characteristics of the two branches of Valley Creek, Minnesota. Values in parentheses are standard deviations.

Parameter	North Branch	South Branch
Mean water temperature (°C) September–October 2015	15.1 (3.2)	11.0 (1.5)
Mean water depth September–October 2015 (m)	0.33 (0.03)	0.21 (0.003)
Mean dissolved phosphorus (µg/L) 1998–2013*	16.2 (19.7)	15.3 (11.5)
Mean dissolved nitrogen (mg/L) 1998–2013*	2.3 (0.6)	6.3 (0.7)
Mean daily discharge (m^3/s) 1998–2015*	0.16 (0.07)	0.24 (0.08)
Vertical hydraulic gradient September–October 2015	0.48 (0.03)	0.10 (0.08)
Surface water NO3–N (mg/L) September–October 2015	3.1 (0.9)	5.2 (2.2)
Groundwater NO3–N October 2015 (mg/L)	1.2	1.1
Surface water dissolved PO4 (µg/L) September–October 2015	2.7 (1.9)	3.5 (1.6)
Groundwater dissolved PO4 (µg/L) October 2015	0	1.5
Surface water dissolved oxygen October 15 (mg/L) [% saturation]	10.6 [93%]	11.0 [95.1]
Groundwater dissolved oxygen October 15 (mg/L) [% saturation]	1.2 [10.8%]	2.6 [23.0%]
Surface water pH October 15 (mg/L)	8.0	8.0
Groundwater pH October 15 (mg/L)	7.3	7.2
Surface water conductivity (µS/cm)	514	580
Groundwater conductivity (µS/cm)	510	501
Mean critical shear stress (τcr, newtons/m^2)	3.63 (1.41)	0.65 (0.55)
Mean sediment size ()	−0.43 (1.00)	−1.14 (1.07)

*Data from Washington County and the St. Croix Watershed Research Station.

Table 2. Macroinvertebrate density and feeding habits. Values in parentheses are standard deviations.

	Mean density (number/m^2)
Taxon	North Branch	South Branch	Feeding habit
Baetidae	8.3 (16.7)	0	Collector gatherer/scraper
Chironomidae	0	2.8 (5.6)	Unknown subfamily
Coenagrionidae	2.8 (5.6)	0	Predator
Elmidae	2.8 (5.6)	5.6 (6.4)	Scraper/collector gatherer
Gammaridae	22.2 (30.1)	1,744 (770.4)	Collector-gatherer
Glossosomatidae	0	8.3 (16.7)	Scraper
Hirudinea*	2.8 (5.6)	0	Unknown family
Hydropsychidae	2.8 (5.6)	0	Collector–filter
Lepidostomatidae	0	13.9 (21.0)	Shredder
Oligochaeta*	2.8 (5.6)	0	Unknown family
Planariidae	5.6 (6.4)	0	Predator
Simuliidae	2.8 (5.6)	0	Collector–filter
Sphaeriidae	2.8 (5.6)	0	Collector–filter

*Only identified to class level.

Table 3. Fishes collected from Valley Creek with dip netting and electroshocking.

Species	North Branch	South Branch
Black crappie (Pomoxis nigromaculatus)	5	0
Bluegill (Lepomis macrochirus)	25	0
Brook stickleback (Culaea inconstans)	4	0
Brown trout (Salmo trutta)	3	23
Brook trout (Salvelinus fontinalis)	0	3
Rainbow trout (Oncorhynchus mykiss)	1	1
Slimy sculpin (Cottus cognatus)	0	122
Yellow bullhead (Ameiurus natalis)	1	0
Total # individuals	39	149

Table 4. Biological characteristics of two branches of Valley Creek, Minnesota.

Parameter	North Branch	South Branch
Mean macroinvertebrate density, #/m^2 (std. dev.)	58.3 (102.0)	1775.0 (771.5)
Macroinvertebrate richness, number of families	10	6
Macroinvertebrate diversity (variance)	1.92 (0.05)	0.12 (0.008)
Macroinvertebrate FBI	5.57 (Fair)	5.94 (Fairly poor)
Number of fish/m	0.35	1.35
Number of fish species	6	4
Fish diversity (variance)	1.17 (0.03)	0.56 (0.005)
Fish IBI	55 (Fair)	105 (Excellent)

Figure 2. Mean leaf decomposition rates as loss of dry weight for two species of leaves (black cherry and common buckthorn) from two locations in Valley Creek, MN over two time periods. Vertical lines show one standard deviation from the mean.

Figure 3. Mean periphyton production rate, measured as chlorophyll a changes, from two locations in Valley Creek, MN over two time periods. The potential for nutrient limitation influencing production was examined by comparing a control (C) with treatments of enrichment with nitrogen (N), phosphorus (P), or both (N + P). Vertical lines show one standard deviation from the mean.

Figure 4. Per cent oxygen saturation (taken at 15-min intervals) for two locations in Valley Creek, MN. Upper panel represents the North Branch; lower panel represents the South Branch. Gaps in the graphs are due to instrument malfunctions.

Figure 5. Temporal changes in daily measures of stream metabolism (measured as mg O₂ m⁻² d⁻¹) at two locations in Valley Creek, MN. Top panel represents gross primary production (GPP), middle panel represents ecosystem respiration (ER), and the bottom panel represents net ecosystem production (NEP). Gaps in the graphs are due to instrument malfunctions.

Table 5. Comparison of abiotic, structural, and functional measures of the two Valley Creek branches.

Parameter	North Branch	South Branch
Abiotic
Mean dissolved phosphorus 1998–2013	↔	↔
Mean dissolved nitrogen 1998–2013	↓	↑
Mean daily discharge (m^3/s) 1998–2015	↓	↑
Vertical hydraulic gradient September–October 2015	↑	↓
Water temperature (°C) September–October 2015	↑	↓
Surface water dissolved oxygen September--October 2015 [% saturation]	↓	↑
Shear stress	↑	↓
Light	↑	↓
Structural
Mean macroinvertebrate density	↓	↑
Macroinvertebrate richness (# species)	↑	↓
Macroinvertebrate diversity	↑	↓
Macroinvertebrate IBI	↑	↓
Feeding guild diversity	↑	↓
Number of fish	↓	↑
Number of fish species	↑	↓
Fish diversity	↑	↓
Fish IBI	↓	↑
Functional
Leaf decomposition	↔	↔
Periphyton – control	↑	↓
Metabolism
GPP	↓	↑
ER	↓	↑
NEP	↑	↓
Heterotrophic	↓	↑