Litter Dynamics Along Stream, Riparian and Upslope Areas Following Hurricane Hugo, Luquillo Experimental Forest, Puerto Rico

Litter Dynamics Along Stream, Riparian and Upslope Areas Following Hurricane Hugo, Luquillo Experimental Forest, Puerto Rico
K. A. Vogt, D. J. Vogt, P. Boon, A. Covich, F. N. Scatena, H. Asbjornsen, J. L. O'Harra, J. Perez, T. g. Siccama, J. Bloomfield and J. F. Ranciato
Vol. 28, No. 4, Part A. Special Issue: Long Term Responses of Caribbean Ecosystems to Disturbances (Dec., 1996), pp. 458-470

Litterfall (fine and coarse) due to Hurricane Hugo and subsequent fine annual litterfall inputs (1, 2 and 5 yr after Hugo) were determined for two sites (El Verde and Bisley) in the Luquillo Experimental Forest in Puerto Rico. Litter transfers into streams, riparian and upslope areas were determined within each catchment. The recovery rate of aboveground fine litterfall (leaf, fine wood <1 cm diameter, and other miscellaneous inputs) to predisturbance levels were determined 1, 2, and 5 yr after Hurricane Hugo. The amount of total litter transfers and their individual components into the riparian and upslope areas due to Hurricane Hugo varied significantly by catchments within the Luquillo Experimental Forest. At El Verde, 26-39 percent, 31-35 percent, 14-35 percent and 7-12 percent of the total litter transfers were contributed by leaf litter, fine wood, coarse wood and fine roots, respectively. At Bisley, 28-31 percent, 26-29 percent, 33-35 percent and 8-10 percent of the litter transfers were contributed by the same categories. Differential decay rates contributed to the relative importance of fine and coarse litter inputs. The recovery of fine aboveground litterfall to pre-hurricane levels after 5 yr varied by topographic location (streams had the slowest recovery, upslope areas the highest) and catchment (El Verde: 55-77%; Bisley: 39-82% of pre-hurricane values).

Suppression of methanogenesis by dissimilatory Fe(III)- reducing bacteria in tropical rain forest soils: implications for ecosystem methane flux

Teh, Y.A., Dubinsky, E.A., Silver, W.L., and Carlson, C.M.
(2008) Suppression of methanogenesis by dissimilatory Fe
(III)-reducing bacteria in tropical rain forest soils: implications
for ecosystem methane flux. Glob Change Biol 14:

Tropical forests are an important source of atmospheric methane (CH4), and recent work suggests that CH4 fluxes from humid tropical environments are driven by variations in CH4 production, rather than by bacterial CH4 oxidation. Competition for acetate between methanogenic archaea and Fe(III)-reducing bacteria is one of the principal controls on CH4 flux in many Fe-rich anoxic environments. Upland humid tropical forests are also abundant in Fe and are characterized by high organic matter inputs, steep soil oxygen (02) gradients, and fluctuating redox conditions, yielding concomitant methanogenesis and bacterial Fe(III) reduction. However, whether Fe(III)-reducing bacteria coexist with methanogens or competitively suppress methanogenic acetate use in wet tropical soils is uncertain. To address this question, we conducted a process-based laboratory experiment to determine if competition for acetate between methanogens and Fe(III)-reducing bacteria influenced CH4 production and C isotope composition in humid tropical forest soils. We collected soils from a poor to moderately drained upland rain forest and incubated them with combinations of C-13-bicarbonate, C-13-methyl labeled acetate ((CH3COO-)-C-13), poorly crystalline Fe(III), or fluoroacetate. CH4 production showed a greater proportional increase than Fe2+ production after competition for acetate was alleviated, suggesting that Fe(III)-reducing bacteria were suppressing methanogenesis. Methanogenesis increased by approximately 67 times while Fe2+ production only doubled after the addition of (CH3COO-)-C-13. Large increases in both CH4 and Fe2+ production also indicate that the two process were acetate limited, suggesting that acetate may be a key substrate for anoxic carbon (C) metabolism in humid tropical forest soils. C isotope analysis suggests that competition for acetate was not the only factor driving CH4 production, as C-13 partitioning did not vary significantly between (CH3COO-)-C-13 and (CH3COO-)-C-13 + Fe(III) treatments. This suggests that dissimilatory Fe(III)-reduction suppressed both hydrogenotrophic and aceticlastic methanogenesis. These findings have implications for understanding the CH4 biogeochemistry of highly weathered wet tropical soils, where CH4 efflux is driven largely by CH4 production.

The Effects of Natural and Human Disturbances on Soil Nitrogen Dynamics and Trace Gas Fluxes in a Puerto Rican Wet Forest

The Effects of Natural and Human Disturbances on Soil Nitrogen Dynamics and Trace Gas Fluxes in a Puerto Rican Wet Forest
P. A. Steudler, J. M. Melillo, R. D. Bowden, M. S. Castro and A. E. Lugo
Vol. 23, No. 4, Part A. Special Issue: Ecosystem, Plant, and Animal Responses to Hurricanes in the Caribbean (Dec., 1991), pp. 356-363

We examined the effects of two disturbances (Hurricane Hugo and forest clearcutting) on soil nitrogen dynamics and on the exchanges of N20, CO,, and CH, between soils and the atmosphere of a subtropical wet forest in Puerto Rico. The disturbances resulted in prolonged increases in ammonium pools and short-term increases in rates of net N-mineralization and net nitrification. Nitrous oxide emissions increased following both disturbances. The most dramatic increase was observed 4 mo after clearcutting; N 2 0 emissions (109.49 pg N/m2-hr) from the cut plot were about two orders of magnitude higher than emissions from the reference plot (1.71 pg N/m2-hr). Carbon dioxide emissions from both disturbed plots (mean 102.47 mg C/m2-hr) were about 30 percent lower than the reference (mean 15 1.28 mg C/m2-hr). Soils at all sites were generally sinks for CH,. Methane uptake, however, was suppressed by both disturbances. This suppression may be related to disturbance-induced changes in the nitrogen cycle, as we have previously observed in temperate zone forests.

Soil Oxygen Availability and Biogeochemistry along Rainfall and Topographic Gradients in Upland Wet Tropical Forest Soils

Silver W, Lugo AE, Keller M (1999) Soil oxygen availability and
biogeochemistry along rainfall and topographical gradients in
upland wet tropical forest soils. Biogeochemistry 44:301–

We measured soil oxygen concentrations at 10 and 35 cm depths and indices of biogeochemical cycling in upland forest soils along a rainfall and elevation gradient (3500– 5000 mm y−1; 350–1050 masl) and along topographic gradients (ridge to valley, 150 m) in the Luquillo Experimental Forest, Puerto Rico. Along the rainfall gradient, soil O2 availability decreased significantly with increasing annual rainfall, and reached very low levels (<3%) in individual chambers for up to 25 consecutive weeks over 82 weeks of study. Along localized topographic gradients, soil O2 concentrations were variable and decreased significantly from ridges to valleys. In the valleys, up to 35% of the observations at 10–35 cm depth were <3% soil O2. Cross correlation analyses showed that soil O2 concentrations were significantly positively correlated along the topographic gradient, and were sensitive to rainfall and hydrologic output. Soil O2 concentrations in valley soils were correlated with rainfall from the previous day, while ridge sites were correlated with cumulative rainfall inputs over 4 weeks. Soils at the wettest point along the rainfall gradient had very high soil methane concentrations (3–24%) indicating a strong influence of anaerobic processes.We measured net methane emission to the atmosphere at the wettest sites of the rainfall gradient, and in the valleys along topographic gradients. Other measures of biogeochemical function such as soil organic matter content and P availability were sensitive to chronic O2 depletion along the rainfall gradient, but less sensitive to the variable soil O2 environment exhibited at lower elevations along topographic gradients.

Nutrient availability in a montane wet tropical forest: Spatial patterns and methodological considerations

Silver, W.L., F.N. Scatena, A.H. Johnson, T.G. Siccama, and M.J.
Sanchez. 1994. Nutrient availability in a montane wet tropical forest: Spatial patterns and methodological considerations. Plant Soil 164:129–145.

Soils and forest floor were sampled quantitatively from a montane wet tropical forest in Puerto Rico to determine the spatial variability of soil nutrients, the factors controlling nutrient availability to vegetation, and the distribution of nutrients in soil and plants. Exchangeable cation concentrations were measured using different soil extracting procedures (fresh soil with NH4C1, air-dried and ground soil with KC1, and a Modified Olsen solution) to establish a range of nutrient availability in the soil, and to determine the relationship between different, but commonly used laboratory protocols. The availability of exchangeable Ca, Mg, and K was significantly lower in soils extracted fresh with NHaCI than from soils which were dried and ground prior to extraction with KCI or a modified Olsen solution. Soil nutrient availability generally decreased with depth in the soil. Several soil properties important to plant growth and survival varied predictably across the landscape and could be viewed in the context of a simple catena model. In the surface soils, exchangeable base cation concentrations and pH increased along a gradient from ridge tops to riparian valleys, while soil organic matter, exchangeable Fe and acidity decreased along this gradient. On the ridges, N, P, and K were positively correlated with soil organic matter; on slopes, N and P were positively correlated with organic matter, and Ca, Kg, and pH were negatively correlated with exchangeable Fe. Nutrient availability in the upper catena appears to be primarily controlled by biotic processes, particularly the accumulation of organic matter. The Ca, K, and P content of the vegetation was higher on ridges and slopes than in the valley positions. Periodic flooding and impeded drainage in the lower catena resulted in a more heterogeneous environment. A comparison of the Bisley, Puerto Rico soils with other tropical montane forests (TMF) revealed that the internal heterogeneity of soils in the Bisley Watersheds is similar to the range of average soil nutrient concentrations among TMF's for Ca, Mg, and K (dry/ground soils). Phosphorus tended to be slightly higher in Bisley and N was lower than in other TMFs.

Comparison of total mercury and methylmercury cycling at five sites using the small watershed approach

Shanley JB, Mast MA et al (2006) Comparison of total mercury and methylmercury cycling at five sites using the small watershed approach. In: 8th international conference on mercury as a global pollutant, Madison, WI

The small watershed approach is well-suited but underutilized in mercury research. We applied the small watershed approach to investigate total mercury (THg) and methylmercury (MeHg) dynamics in streamwater at the five diverse forested headwater catchments of the US Geological Survey Water, Energy, and Biogeochemical Budgets (WEBB) program. At all sites, baseflow THg was generally less than 1 ng L1 and MeHg was less than 0.2 ng L1. THg and MeHg concentrations increased with streamflow, so export was primarily episodic. At three sites, THg and MeHg concentration and export were dominated by the particulate fraction in association with POC at high flows, with maximum THg (MeHg) concentrations of 94 (2.56) ng L1 at Sleepers River, Vermont; 112 (0.75) ng L1 at Rio Icacos, Puerto Rico; and 55 (0.80) ng L1 at Panola Mt., Georgia. Filtered (<0.7 mm) THg increased more modestly with flow in association with the hydrophobic acid fraction (HPOA) of DOC, with maximum filtered THg concentrations near 5 ng L1 at both Sleepers and Icacos. At Andrews Creek, Colorado, THg export was also episodic but was dominated by filtered THg, as POC concentrations were low. MeHg typically tracked THg so that each site had a fairly constant MeHg/THg ratio, which ranged from near zero at Andrews to 15% at the low-relief, groundwater-dominated Allequash Creek,Wisconsin. Allequash was the only site with filtered MeHg consistently above detection, and the filtered fraction dominated both THg and MeHg. Relative to inputs in wet deposition, watershed retention of THg (minus any subsequent volatilization) was 96.6% at Allequash, 60% at Sleepers, and 83% at Andrews. Icacos had a net export of THg, possibly due to historic gold mining or frequent disturbance from landslides. Quantification and interpretation of Hg dynamics was facilitated by the small watershed approach with emphasis on event sampling.  2008 Elsevier Ltd. All rights reserved.

Effects of Hurricane Disturbance on Stream Water Concentrations and Fluxes in Eight Tropical Forest Watersheds of the Luquillo Experimental Forest, Puerto Rico

SCHAEFER, DOUGLAS. A.; McDOWELL, WILLIAM H.; SCATENA, FREDRICK N.; ASBURY,CLYDE E. 2000. Effects of hurricane disturbance on stream water concentrations and fluxes in eight tropical forest watersheds of the Luquillo Experimental Forest, Puerto Rico. . Journal of Tropical Ecology 16:189-207

Stream water chemistry responds substantially to watershed disturbances, but hurricane effects have not been extensively investigated in tropical regions. This study presents a long-term (2.5-1 1 y) weekly record of stream water chemistry on eight forested watersheds (catchment basins) in the Luquillo Mountains of Puerto Rico. This includes a period before and at least 2 y after the disturbance caused by the 1989 Hurricane Hugo. Nitrate, potassium and ammonium concentrations increased after the hurricane and remained elevated for up to 2 y. Sulphate, chloride, sodium, magnesium and calcium showed smaller relative significant changes. Average stream water exports of potassium, nitrate and ammonium increased by 13.1, 3.6 and 0.54 kg ha-' y-' in the first post-hurricane year across all watersheds. These represent increases of 119, 182 and 102% respectively, compared to the other years of record. The increased stream outputs of potassium and nitrogen in the first 2 y post-hurricane are equivalent to 3% (potassium) and 1% (nitrogen) of the hurricanederived plant litter. Effects of hurricanes on tropical stream water potassium and nitrogen can be greater than those caused by canopy gaps or limited forest cutting, but less than those following large-scale deforestation or fire.

Geomorphology, disturbance, and the soil and vegetation of two subtropical wet steepland watersheds of Puerto Rico

F.N. Scatena, Ariel E. Lugo 1995. Geomorphology, disturbance, and the soil and vegetation of two subtropical wet steepland watersheds of Puerto Rico.. Geomorphology 13 :199-213.

Relationships between landforms, soil nutrients, forest structure, and the relative importance of different disturbances were quantified in two subtropical wet steepland watersheds in Puerto Rico. Ridges had fewer landslides and treefall gaps, more above-ground biomass, older aged stands, and greater species richness than other landscape positions. Ridge soils had relatively low quantities of exchangeable bases but high soil organic matter, acidity and exchangeable iron. Valley sites had higher frequencies of disturbance, less biomass, younger aged stands, lower species richness and soils with more exchangeable bases.Soil N, P, and K were distributed relatively independently of geomorphic setting, but were significantly related to the composition and age of vegetation. On a watershed basis, hurricanes were the dominant natural disturbance in the turnover of individuals, biomass, and forest canopy. However, turnover by the mortality of individuals that die without creating canopy openings was faster than the turnover by any natural disturbance. Only in riparian areas was forest turnover by treefall gaps faster than turnover by hurricanes. The same downslope mass transfer that links soil forming processes across the landscape also influences the distribution of landslides, treefall gaps, and the structure and composition of the forest. One consequence of these interactions is that the greatest aboveground biomass occurs on ridges where the soil nutrient pools are the smallest. Geomorphic stability, edaphic conditions, and biotic adaptations apparently override the importance of spatial variations in soil nutrients in the accumulation of above-ground biomass at this site.

Control of Nitrogen Export from Watersheds by Headwater Streams

Peterson, B.J. et al. 2001. Control of Nitrogen Export from Watersheds by Headwater Streams.
Science 6 April 2001:
Vol. 292 no. 5514 pp. 86-90
DOI: 10.1126/science.1056874

A comparative 15N-tracer study of nitrogen dynamics in headwater streams from biomes throughout North America demonstrates that streams exert control over nutrient exports to rivers, lakes, and estuaries. The most rapid uptake and transformation of inorganic nitrogen occurred in the smallest streams. Ammonium entering these streams was removed from the water within a few tens to hundreds of meters. Nitrate was also removed from stream water but traveled a distance 5 to 10 times as long, on average, as ammonium. Despite low ammonium concentration in stream water, nitrification rates were high, indicating that small streams are potentially important sources of atmospheric nitrous oxide. During seasons of high biological activity, the reaches of headwater streams typically export downstream less than half of the input of dissolved inorganic nitrogen from their watersheds.

Forest Floor Decomposition Following Hurricane Litter Inputs in Several Puerto Rican Forests

Rebecca Ostertag, Frederick N. Scatena, and Whendee L. Silver. 2003. Forest Floor Decomposition Following Hurricane Litter Inputs in Several Puerto Rican Forests. Ecosystems 6 :261-273.

Hurricanes affect ecosystem processes by altering resource availability and heterogeneity, but the spatial and temporal signatures of these events on biomass and nutrient cycling processes are not well understood. We examined mass and nutrient inputs of hurricane-derived litter in six tropical forests spanning three life zones in northeastern Puerto Rico after the passage of Hurricane Georges. We then followed the decomposition of forest floor mass and nutrient dynamics over 1 year in the three forests that experienced the greatest litter inputs (moist, tabonuco, and palm forests) to assess the length of time for which litter inputs influence regeneration and nutrient cycling processes. The 36-h disturbance event had litterfall rates that ranged from 0.55 to 0.93 times annual rates among the six forests; forest floor ranged between 1.2 and 2.5 times prehurricane standing stocks. The upperelevation forest sites had the lowest nonhurricane litterfall rates and experienced the lowest hurricane litterfall and the smallest relative increase in forest floor standing stocks. In the three intensively studied forests, the forest floor returned to prehurricane values very quickly, within 2–10 months. The palm forest had the slowest rate of decay (k  0.74  0.16 y–1), whereas the tabonuco forest and the moist forest had similar decay rates (1.04  0.12 and 1.09  0.14, respectively). In the moist forest, there were short-term increases in the concentrations of nitrogen (N), hosphorus (P), calcium (Ca), and magnesium (Mg) in litter, but in the other two forests nutrient concentrations generally decreased. The rapid disappearance of the hurricane inputs suggests that such pulses are quickly incorporated into nutrient cycles and may be one reason for the extraordinary resilience of these forests to wind disturbances.
Syndicate content