Effects of small-scale armoring and residential development on the salt marsh/upland ecotone

By Alyssa-Lois M. Gehman, Natalie A. McLenaghan, James E. Byers, Clark R. Alexander, Steven C. Pennings and Merryl Alber

Supplementary Information S1

Question 1 (supplemental support): How does land-use category affect the physical and environmental characteristics of the upper marsh?

Soil Core Methods: Sediment core samples were collected with a 30-cm long push corer between the two transects. Surface samples represented the upper 2 cm of the marsh surface, whereas the cores were sectioned into 5-cm thick intervals down to 30 cm. All sediment samples were wet-sieved using standard protocol through a 63 µm (4-phi) sieve (Alexander et al., 1986). The coarse fraction (>63 µm ) was then dried and sieved through stacked sieves starting at -1 phi (2 mm) to separate gravel (larger than 2 mm) from sand (2 mm - 63 µm) at 0.25 phi intervals. The percentage of mud (<63 µm ) was quantified drying an aliquot. If sufficient quantities of mud existed (>10% by weight), the silt and clay grain-size distributions were determined with a Micromeritics Sedigraph 5100. If the sample contained <10 % mud, an additional aliquot was taken to quantify the percent silt and clay in the sample. Sediment statistics (e.g., mean, size and sorting (standard deviation) were derived from these data using the method of moments (Griffiths, 1967). Core samples were described using the grain size nomenclature of Folk (1980) to illustrate broad-scale, downcore trends.

Results: Soil core grain size data were analyzed using multinomial logistic regression with grain size nomenclature as the response variable and land-use category and depth in the core and their interaction as predictor variables.

Table S1.1 Multinomial regression of the probability of finding muddy sand, silty clay or sandy mud (compared to sand) depending on the adjacent land-use category, the depth in the soil and the relationship between interval and land-use category.

Muddy Sand / Silty Clay / Sandy Mud
Intercept / -0.82 / -16.43a / -2.20a
Armored to Unarmored / -0.38a / -10.03a / 0.33a
Forested to Armored / 0.61 / 12.16a / 0.47
Forested to Unarmored / 0.22 / 3.31 / 0.80
Depth / 0.05a / -0.18 / 0.04
Armored to Unarmored:Depth / 0.04 / 23.21 / 0.05
Forested to Armored:Depth / -0.06 / 0.29 / -0.02
Forested to Unarmored:Depth / -0.05 / -0.03 / 0.00
AIC / 724.90

a Significant at p < 0.05

Figure S1.1 Distribution of soil types from 2m pushcores by depth and land-use categories. The width of each row (eg. distance between 0 and 5 on the y-axis) is proportional to the number of responses in each category. The x-axis refers to the proportion of samples adjacent to that land-use category that were in each soil category. For example, for samples from the forest site between 20 and 25cm ~58% of them were Muddy sand ~30% were sand and the final 12% were sandy mud.


Appendix S2

Table S2.2 Two linear mixed-effects models evaluating the relationships between the proportion of bare mud and the concentration of ammnonia or phosphate, with Station as a random variable and bare mud and upland site type as fixed variables.

Variable / NH4 / PO4
Variance / Station / 50.94 / 2.28
β Coefficients / Intercept / 6.54 / 2.47
Bare mud / 20.81a / 9.9a
Forested:Unarmored / -9.57 / -0.75
Unarmored:Armored / -1.44 / -1.94
Forested: Armored / 8.13 / -1.19

a Significant at p < 0.05

Figure S2.2: High levels of ammonia and phosphate found at the forested sites were positively correlated with increased bare substrate.


Appendix S3

Question 4 (Supplemental support): How does land-use category affect the use of terrestrial habitats by organisms that routinely move between the upland and marsh?

Methods

We conducted a pitfall trap survey to better quantify the number and distance that crabs move into the upland at each of the three land use types surveyed. We placed five pitfall trap transects at each of the three locations, an armored site, an unarmored site and a forested site. All locations were within a kilometer of each other on the south end of the Sapelo Island, GA, near the University of Georgia Marine Institute. On July 16th 2013, we dug holes and placed pitfall traps (with a wet sponge) at 2, 4 and 8 meters into the upland from either the bulkhead or zero line (as determined in the survey) on each trap transect. We left traps for 48 hours and on July 18th 2013 we collected traps, bringing all crabs in the pitfall traps back to the lab for quantification. The pitfall trap survey does not have any true replication (only one replicate at each land-use category), so we did not perform statistical analyses.

Results: We found the most Armases in the upland and the furthest into the upland at the forested sites, followed by the unarmored sites and finally the armored sites. At all locations the number of Armases found in the traps decreased as we moved further into the upland.

Figure S3.1 The number of crabs moving from the marsh into the upland by the experimental treatments. Standard errors are from five transect lines run at a single site for each land-use category.

Appendix S4

Table S5.1-4 Mean, standard deviation (SD) and minimum (Min) and maximum (Max) values for each response variable collected through our survey summarized by land-use category and sampling point along the transect (2, 4 or 8 m from the upland).


Table S5.1

Response / Upland Type / Distance from Upland / Mean / SD / Min / Max
bare mud / Armored / 2 / 1.88 / 3.15 / 0.00 / 13.50
bare mud / Forested / 2 / 11.68 / 24.94 / 0.00 / 96.00
bare mud / Unarmored / 2 / 2.88 / 7.19 / 0.00 / 24.50
bare mud / Armored / 4 / 1.70 / 2.23 / 0.00 / 7.50
bare mud / Forested / 4 / 8.23 / 14.94 / 0.00 / 58.00
bare mud / Unarmored / 4 / 0.95 / 2.72 / 0.00 / 10.00
bare mud / Armored / 8 / 6.65 / 19.62 / 0.00 / 88.00
bare mud / Forested / 8 / 10.48 / 16.42 / 0.00 / 50.00
bare mud / Unarmored / 8 / 7.80 / 22.23 / 0.00 / 100.00
Elevation / Armored / 2 / 1.00 / 0.10 / 0.82 / 1.21
Elevation / Forested / 2 / 1.12 / 0.16 / 0.88 / 1.42
Elevation / Unarmored / 2 / 1.10 / 0.16 / 0.87 / 1.45
Elevation / Armored / 4 / 0.87 / 0.15 / 0.46 / 1.22
Elevation / Forested / 4 / 0.97 / 0.18 / 0.65 / 1.31
Elevation / Unarmored / 4 / 0.95 / 0.12 / 0.71 / 1.11
Elevation / Armored / 8 / 0.74 / 0.23 / 0.27 / 1.21
Elevation / Forested / 8 / 0.80 / 0.22 / 0.32 / 1.15
Elevation / Unarmored / 8 / 0.78 / 0.17 / 0.50 / 1.05
Mud / Armored / 2 / 22.09 / 16.53 / 2.75 / 68.08
Mud / Forested / 2 / 15.88 / 10.72 / 5.23 / 38.50
Mud / Unarmored / 2 / 26.98 / 18.73 / 3.50 / 70.39
Mud / Armored / 4 / 41.04 / 22.44 / 9.67 / 88.64
Mud / Forested / 4 / 25.62 / 20.61 / 8.20 / 83.01
Mud / Unarmored / 4 / 39.44 / 31.11 / 6.87 / 94.05
Mud / Armored / 8 / 67.67 / 27.26 / 6.25 / 94.95
Mud / Forested / 8 / 43.77 / 27.93 / 7.29 / 95.99
Mud / Unarmored / 8 / 36.03 / 27.86 / 7.05 / 92.30
Sand / Armored / 2 / 77.91 / 16.53 / 31.92 / 97.25
Sand / Forested / 2 / 84.93 / 9.97 / 61.50 / 94.77
Sand / Unarmored / 2 / 80.70 / 13.86 / 56.34 / 96.50
Sand / Armored / 4 / 58.96 / 22.44 / 11.36 / 90.33
Sand / Forested / 4 / 73.60 / 21.14 / 16.99 / 91.80
Sand / Unarmored / 4 / 63.85 / 27.08 / 10.13 / 92.34
Sand / Armored / 8 / 32.33 / 27.26 / 5.05 / 93.75
Sand / Forested / 8 / 54.14 / 27.44 / 4.01 / 92.71
Sand / Unarmored / 8 / 39.95 / 31.05 / 5.95 / 92.95
water content / Armored / 2 / 0.41 / 0.10 / 0.28 / 0.65
water content / Forested / 2 / 0.38 / 0.10 / 0.25 / 0.60
water content / Unarmored / 2 / 0.43 / 0.14 / 0.25 / 0.68
water content / Armored / 4 / 0.49 / 0.10 / 0.34 / 0.72
water content / Forested / 4 / 0.45 / 0.14 / 0.25 / 0.70
water content / Unarmored / 4 / 0.51 / 0.19 / 0.25 / 0.80
water content / Armored / 8 / 0.54 / 0.14 / 0.22 / 0.75
water content / Forested / 8 / 0.50 / 0.13 / 0.26 / 0.69
water content / Unarmored / 8 / 0.58 / 0.18 / 0.25 / 0.81

Table S5.2

Response / Upland Type / Distance from Upland / Mean / SD / Min / Max
NH4 / Armored / 2 / 17.63 / 18.97 / 0.60 / 61.80
NH4 / Forested / 2 / 26.96 / 37.33 / 0.80 / 156.70
NH4 / Unarmored / 2 / 17.09 / 27.39 / 0.50 / 120.40
NH4 / Armored / 4 / 15.53 / 29.70 / 1.90 / 128.90
NH4 / Forested / 4 / 30.72 / 33.08 / 2.00 / 115.10
NH4 / Unarmored / 4 / 21.73 / 25.93 / 0.50 / 82.00
NH4 / Armored / 8 / 24.73 / 25.00 / 1.50 / 79.30
NH4 / Forested / 8 / 31.72 / 31.55 / 2.30 / 102.90
NH4 / Unarmored / 8 / 21.03 / 30.33 / 0.90 / 114.80
NO3 / Armored / 2 / 4.27 / 12.10 / 0.10 / 53.20
NO3 / Forested / 2 / 24.47 / 86.17 / 0.30 / 378.10
NO3 / Unarmored / 2 / 25.03 / 78.01 / 0.40 / 336.00
NO3 / Armored / 4 / 1.04 / 1.23 / 0.20 / 5.20
NO3 / Forested / 4 / 1.24 / 1.36 / 0.10 / 5.30
NO3 / Unarmored / 4 / 3.11 / 6.49 / 0.10 / 24.60
NO3 / Armored / 8 / 0.64 / 0.56 / 0.00 / 2.20
NO3 / Forested / 8 / 1.09 / 1.68 / 0.00 / 6.10
NO3 / Unarmored / 8 / 0.65 / 0.54 / 0.00 / 1.60
PO4 / Armored / 2 / 3.95 / 6.28 / 0.00 / 20.60
PO4 / Forested / 2 / 5.68 / 6.03 / 0.20 / 22.70
PO4 / Unarmored / 2 / 4.24 / 6.57 / 0.10 / 21.70
PO4 / Armored / 4 / 6.66 / 7.06 / 0.00 / 20.60
PO4 / Forested / 4 / 5.58 / 6.67 / 0.30 / 28.00
PO4 / Unarmored / 4 / 6.52 / 10.02 / 0.00 / 41.20
PO4 / Armored / 8 / 15.05 / 17.47 / 0.00 / 58.40
PO4 / Forested / 8 / 15.31 / 16.60 / 0.50 / 64.70
PO4 / Unarmored / 8 / 12.32 / 13.78 / 0.00 / 58.20
Salinity / Armored / 2 / 21.10 / 9.42 / 2.50 / 35.50
Salinity / Forested / 2 / 21.43 / 6.19 / 9.00 / 34.50
Salinity / Unarmored / 2 / 19.85 / 9.31 / 2.00 / 35.00
Salinity / Armored / 4 / 23.83 / 11.70 / 5.00 / 52.50
Salinity / Forested / 4 / 24.03 / 6.76 / 8.50 / 32.50
Salinity / Unarmored / 4 / 21.45 / 8.59 / 3.00 / 34.00
Salinity / Armored / 8 / 27.38 / 10.41 / 5.50 / 44.50
Salinity / Forested / 8 / 25.90 / 6.43 / 13.00 / 35.50
Salinity / Unarmored / 8 / 24.93 / 7.73 / 9.00 / 39.50
soil OM / Armored / 2 / 0.16 / 0.13 / 0.02 / 0.50
soil OM / Forested / 2 / 0.13 / 0.12 / 0.03 / 0.40
soil OM / Unarmored / 2 / 0.18 / 0.17 / 0.02 / 0.65
soil OM / Armored / 4 / 0.19 / 0.15 / 0.03 / 0.57
soil OM / Forested / 4 / 0.17 / 0.15 / 0.03 / 0.48
soil OM / Unarmored / 4 / 0.26 / 0.23 / 0.02 / 0.77
soil OM / Armored / 8 / 0.29 / 0.22 / 0.02 / 0.80
soil OM / Forested / 8 / 0.27 / 0.22 / 0.05 / 0.73
soil OM / Unarmored / 8 / 0.30 / 0.21 / 0.03 / 0.72

Table S5.3

Response / Upland Type / Distance from Upland / Mean / SD / Min / Max
Borrichia / Armored / 2 / 9.00 / 19.36 / 0.00 / 64.50
Borrichia / Forested / 2 / 11.68 / 30.04 / 0.00 / 100.00
Borrichia / Unarmored / 2 / 23.45 / 38.06 / 0.00 / 100.00
Borrichia / Armored / 4 / 1.23 / 5.48 / 0.00 / 24.50
Borrichia / Forested / 4 / 6.73 / 23.09 / 0.00 / 100.00
Borrichia / Unarmored / 4 / 6.53 / 21.03 / 0.00 / 84.50
Borrichia / Armored / 8 / 1.75 / 7.83 / 0.00 / 35.00
Borrichia / Forested / 8 / 1.28 / 5.70 / 0.00 / 25.50
Borrichia / Unarmored / 8 / 0.00 / 0.00 / 0.00 / 0.00
Juncus / Armored / 2 / 34.68 / 40.13 / 0.00 / 100.00
Juncus / Forested / 2 / 29.63 / 38.38 / 0.00 / 100.00
Juncus / Unarmored / 2 / 31.35 / 42.27 / 0.00 / 100.00
Juncus / Armored / 4 / 21.78 / 37.19 / 0.00 / 100.00
Juncus / Forested / 4 / 33.98 / 39.88 / 0.00 / 100.00
Juncus / Unarmored / 4 / 26.93 / 41.58 / 0.00 / 100.00
Juncus / Armored / 8 / 12.85 / 31.94 / 0.00 / 100.00
Juncus / Forested / 8 / 25.55 / 39.55 / 0.00 / 100.00
Juncus / Unarmored / 8 / 14.33 / 31.66 / 0.00 / 100.00
Spartina / Armored / 2 / 53.65 / 44.34 / 0.00 / 100.00
Spartina / Forested / 2 / 25.25 / 26.64 / 0.00 / 74.00
Spartina / Unarmored / 2 / 24.93 / 32.82 / 0.00 / 100.00
Spartina / Armored / 4 / 64.58 / 41.89 / 0.00 / 100.00
Spartina / Forested / 4 / 46.30 / 40.95 / 0.00 / 98.50
Spartina / Unarmored / 4 / 46.13 / 42.58 / 0.00 / 100.00
Spartina / Armored / 8 / 64.60 / 40.58 / 0.00 / 100.00
Spartina / Forested / 8 / 59.03 / 40.59 / 0.00 / 100.00
Spartina / Unarmored / 8 / 57.90 / 45.51 / 0.00 / 100.00
vegetative fraction / Armored / 2 / 0.47 / 0.26 / 0.05 / 0.90
vegetative fraction / Forested / 2 / 0.27 / 0.30 / 0.01 / 0.98
vegetative fraction / Unarmored / 2 / 0.31 / 0.28 / 0.00 / 0.97
vegetative fraction / Armored / 4 / 0.35 / 0.24 / 0.01 / 0.76
vegetative fraction / Forested / 4 / 0.23 / 0.21 / 0.00 / 0.79
vegetative fraction / Unarmored / 4 / 0.30 / 0.25 / 0.00 / 0.95
vegetative fraction / Armored / 8 / 0.33 / 0.25 / 0.01 / 0.72
vegetative fraction / Forested / 8 / 0.29 / 0.21 / 0.04 / 0.69
vegetative fraction / Unarmored / 8 / 0.24 / 0.25 / 0.00 / 0.85
Wrack / Armored / 2 / 19.63 / 24.59 / 0.00 / 79.50
Wrack / Forested / 2 / 37.00 / 39.88 / 0.00 / 100.00
Wrack / Unarmored / 2 / 36.50 / 41.64 / 0.00 / 96.00
Wrack / Armored / 4 / 29.73 / 40.33 / 0.00 / 100.00
Wrack / Forested / 4 / 28.65 / 37.38 / 0.00 / 100.00
Wrack / Unarmored / 4 / 32.70 / 42.04 / 0.00 / 100.00
Wrack / Armored / 8 / 26.93 / 39.17 / 0.00 / 100.00
Wrack / Forested / 8 / 26.35 / 29.87 / 0.00 / 98.50
Wrack / Unarmored / 8 / 32.43 / 40.05 / 0.00 / 100.00

Table S5.4