Nutrient Inventories Research Articles

A spreadsheet-based biogeochemical model to simulate nutrient cycling processes in forest ecosystems

A Nutrient Cycling Spreadsheet (NuCSS) model was developed to simulate nutrient cycling in forest ecosystems. This model is intended to provide a tool for nutrient management and is intermediate in complexity between simple budget calculations and complex, process-based ecosystem models. NuCSS simulates biomass production, organic matter decomposition, N mineralization, cation adsorption, weathering and leaching (hydrology not included) using empirical relationships and simple mechanistic process descriptions. The model calculates a target biomass production and associated nutrient uptake. By reviewing soil nutrient pools the user can assess whether available soil nutrients can sustain the targeted biomass production. NuCSS was calibrated to a Norway spruce site in the Solling Mountains, Germany. The model performance was evaluated using long-term data on deposition, vegetation, water quality and soil nutrient inventories. Long-term predictions were made using a ‘business as usual’ and two reduced deposition scenarios. Results from NuCSS were compared with simulations from other biogeochemical models. The element distribution over soil, forest floor and vegetation closely matched measurements both after one and 15 years. Forest floor nutrients were underestimated but data on forest floor accumulation proved to be unreliable. NuCSS overestimated N uptake, N mineralization and leaching but not enough data on these fluxes were available to determine whether NuCSS was wrong. Simulated base cation leaching agreed well with the measurements but K leaching was overestimated most likely due to an underestimation of the selectivity coefficient for K adsorption. The reduced deposition scenarios caused N and base cation leaching to decrease with time. When N deposition was reduced by 95%, a N deficit occurred and N mineralization and deposition could not sustain the (fixed) uptake. For most simulated parameters NuCSS agreed well with more detailed, process-based, biogeochemical models. In general, NuCSS simulated a higher N leaching and N mineralization than most other models. Trends in base saturation and base cation leaching simulated by NuCSS agreed well with other models. The model proved to be helpful in addressing some of the uncertainties in nutrient cycling regarding vegetation uptake, weathering rates and N mineralization. Given the uncertainties in description of certain processes, a quantitative use of NuCSS may not be justified. These uncertainties also apply to more complex nutrient cycling models, however.

Ocean stagnation and end-Permian anoxia

Research Article| January 01, 2001 Ocean stagnation and end-Permian anoxia Roberta M. Hotinski; Roberta M. Hotinski 1Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA Search for other works by this author on: GSW Google Scholar Karen L. Bice; Karen L. Bice 2Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA Search for other works by this author on: GSW Google Scholar Lee R. Kump; Lee R. Kump 3Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA Search for other works by this author on: GSW Google Scholar Raymond G. Najjar; Raymond G. Najjar 4Department of Meteorology, Pennsylvania State University, University Park, Pennsylvania 16802, USA Search for other works by this author on: GSW Google Scholar Michael A. Arthur Michael A. Arthur 5Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania 16802, USA Search for other works by this author on: GSW Google Scholar Geology (2001) 29 (1): 7–10. https://doi.org/10.1130/0091-7613(2001)029<0007:OSAEPA>2.0.CO;2 Article history received: 01 May 2000 rev-recd: 21 Sep 2000 accepted: 04 Oct 2000 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Roberta M. Hotinski, Karen L. Bice, Lee R. Kump, Raymond G. Najjar, Michael A. Arthur; Ocean stagnation and end-Permian anoxia. Geology 2001;; 29 (1): 7–10. doi: https://doi.org/10.1130/0091-7613(2001)029<0007:OSAEPA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Ocean stagnation has been invoked to explain the widespread occurrence of organic-carbon–rich, laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end-Permian mass extinction. However, to a first approximation, stagnation would severely reduce the upwelling supply of nutrients to the photic zone, reducing productivity. Moreover, it is not obvious that ocean stagnation can be achieved. Numerical experiments performed with a three-dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low equator to pole temperature gradient could have produced weak oceanic circulation and widespread anoxia in the Late Permian ocean. We find that polar warming and tropical cooling of sea-surface temperatures cause anoxia throughout the deep ocean as a result of both lower dissolved oxygen in bottom source waters and increased nutrient utilization. Buildup of quantities of H2S and CO2 in the Late Permian ocean sufficient to directly cause a mass extinction, however, would have required large increases in the oceanic nutrient inventory. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Upper ocean circulation in the glacial North Atlantic from benthic foraminiferal isotope and trace element fingerprinting

Benthic Cd/Ca and δ13C records from the midlatitude and northern North Atlantic are used to derive nutrient inventories and water mass distribution patterns for the past 50,000 years. Inferred Holocene water column Cd concentrations (CdW′) and δ13C values are 0.17–0.24 nmol kg−1 and 1.0–1.3‰ Peedee belemnite (PDB), which document the dominance of nutrient‐depleted Mediterranean Outflow Water (MOW) and Upper North Atlantic Deep Water (UNADW). Glacial benthic Cd/Ca and δ13C indicate a continued contribution of UNADW to the northern North Atlantic and upper Portuguese margin (CdW′=0.08 nmol kg−1; δ13C=+1.86‰ PDB). At the upper Moroccan margin, glacial CdW′ (0.23 nmol kg−1) is higher, and δ13C (+1.44‰ PDB) is lower. During “Heinrich” events, benthic δ13C decreases by up to 1.3‰, and peak Cd/Ca increases by 0.1–0.14 µmol mol−1; water column phosphorus equivalents are 1.8–2.8 µmol kg−1. The combined Cd/Ca and δ13C pattern indicates that during mean glacial conditions Antarctic Intermediate Water, (AAIW) reached the midlatitude northeast Atlantic (30°N). During Heinrich events, AAIW contribution maximized so that Southern Hemisphere waters filled the North Atlantic basin from bottom water to middepth levels.

WATER QUALITY TRENDS AND MANAGEMENT IMPLICATIONS FROM A FIVE-YEAR STUDY OF A EUTROPHIC ESTUARY

The Neuse River and Estuary, a major tributary of the second largest estuary on the United States mainland, historically has sustained excessive blooms of algae and toxic dinoflagellates, hypoxia, and fish kills. Previous attempts have been made to use short-term databases of 2–3 years, or data sets from infrequent (monthly) sampling, to assess whether nutrient inputs to the Neuse are increasing and supporting higher algal production. These previous efforts also have relied on single-point-determined flow velocity data, at upstream sites remote from the estuary, to estimate the volume of flow in quantifying nutrient loading to the estuary. We completed a five-year study of the Neuse, including a comparative inventory of nutrients to the watershed from point sources and from concentrated animal operations (CAOs) as recent nonpoint sources, as well as an intensive assessment of water quality over time in the mesohaline estuary. Estimates of nutrient loads were based on volume of flow data from shore-to-shor...

Water Quality Trends and Management Implications from a Five-Year Study of a Eutrophic Estuary

The Neuse River and Estuary, a major tributary of the second largest estuary on the United States mainland, historically has sustained excessive blooms of algae and toxic dinoflagellates, hypoxia, and fish kills. Previous attempts have been made to use short-term databases of 2–3 years, or data sets from infrequent (monthly) sampling, to assess whether nutrient inputs to the Neuse are increasing and supporting higher algal production. These previous efforts also have relied on single-point-determined flow velocity data, at upstream sites remote from the estuary, to estimate the volume of flow in quantifying nutrient loading to the estuary. We completed a five-year study of the Neuse, including a comparative inventory of nutrients to the watershed from point sources and from concentrated animal operations (CAOs) as recent nonpoint sources, as well as an intensive assessment of water quality over time in the mesohaline estuary. Estimates of nutrient loads were based on volume of flow data from shore-to-shore transect cross sections, taken with a boat-mounted acoustic Doppler current profiler at the westernmost edge of the estuary. A total of 441 point dischargers contributed at least 3.34 × 108 L effluent/d to the Neuse system, much of which came from municipal wastewater treatment plants (2.03 × 108 L effluent/d, excluding periods of plant malfunctions; total annual loadings of at least 9 × 105 kg P and 2.1 × 106 kg N, with a 17% increase in human population over the past decade). The Neuse basin also included 554 CAOs, with 76% in swine production (1.7 × 106 animals, from a 285% increase in the past decade) and 23% in poultry (5.5 × 105 animals). An estimated 5.9 × 109 kg manure produced by swine and poultry during 1998 contributed ∼4.1 × 107 kg N and 1.4 × 107 kg P to the Neuse watershed. About 20% of the area in the watershed now has enough manure from CAOs to exceed the P requirements of all nonlegume crops and forages. About two-thirds of the N- and P-rich feeds for these animals are imported (with 4.0 × 107 kg N and 1.6 × 107 kg P in 1998); thus, the watershed increasingly has become a nutrient sink. Over the five-year study in the Neuse Estuary study area, P loading significantly declined (by an estimated 14%), whereas TN (total nitrogen) loading significantly increased (by an average of 16%) and TNi (total inorganic nitrogen) increased by ∼38%. The increased inorganic N (Ni), partly related to severe storms with high precipitation in years 4–5, coincided with a decrease in phytoplankton biomass (as chlorophyll a) that likely reflected displacement/washout of algal populations and cysts. Thus, while both N and P supplies have increased in the watershed, there is evidence for a significant increase in Ni loading but, as yet, no apparent signal for increased P in the lower estuary. Weather patterns ultimately control when/whether the elevated Ni supply will support increased algal production, so that estuarine algal blooms, hypoxia, and fish kills will remain difficult, at best, to predict in modeling efforts. We recommend that decadal data sets, with sufficient sampling frequency to capture nutrient loadings from major storm events, be used to assess fluctuations in algal production of lower rivers and estuaries, and relationships with changing nutrient inputs. Given increased N and P supplies in the Neuse watershed from ongoing growth of both human and swine populations, a current management goal of 30% N reduction should be altered to include increased focus on Ni and strengthened comanagement of P. As for estuaries in other regions, nutrient reduction goals should be interpreted as “moving targets” that likely will have to be substantially adjusted upward, over time, to accomplish noticeable reductions in algal blooms, hypoxia, and fish kills in the lower Neuse River and Estuary.

Comparison of interglacial stages in the South Atlantic sector of the southern ocean for the past 450 kyr: implifications for Marine Isotope Stage (MIS) 11

Oxygen and carbon isotopic gradients in surface waters were reconstructed for the past 450 kyr by analysis of the planktic foraminifer Neogloboquadrina pachyderma in cores located at approximately 43°, 47°, and 54°S across the Polar Frontal Zone in the South Atlantic sector of the Southern Ocean. Comparison of the oxygen isotopic records for peak interglacial conditions during the past 450 kyr reveals that Marine Isotope Stage (MIS) 11 was not substantially warmer than other interglacials at high southern latitudes, although the period of warmth lasted longer. The carbonate and carbon isotope chemistry of surface and deep water represent the truly distinctive aspects of Stage 11 in the Southern Ocean. Peak carbonate production occurred at high southern latitudes during MIS 11, resulting in light-colored, high-carbonate sediments deposited throughout the Southern Ocean above the lysocline. Carbon isotopic values of benthic foraminifera in cores bathed by Circumpolar Deep Water (CPDW) were highest during MIS11, suggesting strong input of North Atlantic Deep Water (NADW) to the Southern Ocean. Planktic δ 13C values at high southern latitudes were also highest during MIS 11, which may reflect upwelling of CPDW with a greater contribution of NADW, lower whole-ocean nutrient inventories, higher gas exchange rates, and/or lowered alkalinity of Antarctic surface waters (resulting from carbonate precipitation south of the Polar Front).

Influences of oceanic rheostats and amplifiers on atmospheric CO 2 content during the Late Quaternary

Although a clear explanation has yet to emerge for the observed decline in atmospheric CO 2 content during glacial episodes, numerous hypotheses have been offered. Selected examples are reviewed or evaluated here. A strengthened biological pump resulting from intensified upwelling at low latitudes was suggested early on as a likely direct cause of the glacial CO 2 drawdown. Two problems have since arisen with this hypothesis. First, on some upwelling continental margins, for example off California, Oregon, northwestern Mexico, Peru, and parts of NW Africa, organic matter accumulation decreased, in some areas markedly, during the Last Glacial Maximum (LGM). Second, upwelled cool CO 2-rich water degasses carbon dioxide in warm regions, and for a key area such as the modern equatorial Pacific to become a net sink for atmospheric CO 2, rather than a source as it is today, the rate of downward organic carbon export must exceed the rate of degassing. Recent sedimentary carbon and nitrogen isotopic data suggest however that the equatorial Pacific has remained a strong CO 2 source for at least the last 40,000 yr and probably much longer. Although the direct extraction of carbon from surface waters and burial in the sediments in productive regions now appears unlikely to provide the sought-for explanation, indirect effects related to export productivity may hold the key. These can modulate the chemical character of the ocean so as to increase its uptake of CO 2 (a rheostat effect) or they could increase indirectly the nutrient inventory of the sea (an amplifier effect). For example, it is now recognized that denitrification was greatly reduced during glacial maxima in all three principal oxygen minimum zones in the oceans, i.e. the subtropical north and south Pacific and the Arabian Sea. The implication is that nitrate, the limiting nutrient in the modern ocean, must have been more abundant during glacial periods, and that this surfeit would have supported increased export production in the meso or oligotrophic areas that are today nitrate-limited. Dust may represent another rheostat. Increases in atmospheric turbidity during glacials are clearly recorded by ice and marine sediment cores in both hemispheres. In addition to fostering enhanced export production by adding needed iron to nitrate-rich areas, it has been suggested recently that increased dust inputs to nitrate-depleted regions during glacials might have encouraged growth of iron-hungry N 2 fixing cyanobacteria, thus alleviating nitrate limitation. No sedimentary δ 15 N data yet exist to support this hypothesis, but it remains viable. Finally, regional changes in physical hydrography may have played a major and hitherto underestimated role. For example, in the glacial Southern Ocean south of the Polar Front, recent nitrogen isotope and other data imply that the upper water column was well stratified during the LGM. By limiting upwelling, this would have reduced the ocean-atmosphere CO 2 `leak’ in the area. This could have made a significant contribution to the pCO 2 drawdown.

Benthic flux of biogenic elements on the Southeastern US continental shelf: influence of pore water advective transport and benthic microalgae

In situ, paired light and dark benthic flux chamber incubations were used to estimate the exchange of nutrients, oxygen and inorganic carbon across the sediment – water interface of the South Atlantic Bight (SAB) continental shelf. The results indicate that physically forced non-diffusive pore water transport and benthic primary production (BPP) by sea floor microalgae exert a major influence on benthic exchange rates on the mid- and outer-continental shelf (depths of 14–40 m). Light fluxes to the sea floor and sediment photosynthetic pigment distributions determined on two, widely spaced cross-shelf transects suggest that BPP may occur over 84% of the SAB continental shelf area. Microalgal gross BPP rates at all study sites averaged 400±260 mg C m −2 d −1 between May and September 1996 while water column primary productivity averaged 682±176 mg C m −2 d −1, implying a total primary productivity for this region of approximately 1100 mg C m −2 d −1 (1.6 times the water column productivity alone). The results are also consistent with the advective transport of pore waters. Benthic flux chambers appear to retard this exchange, affecting the accuracy of derived net fluxes. Given our inability to relate pore water gradients to fluxes in non-diffusive regimes and to mimic natural advective transport in intact core incubations, traditional techniques such as pore water gradient diffusion calculations or shipboard core incubations also may not provide accurate flux estimates. Because of these limitations, fundamental questions remain concerning the processes that control nutrient inventories in pore waters and the magnitude of the net benthic flux of nutrients on the sandy SAB shelf.

Productividad en el ejemplo de seis sitios característicos de la VIII Región con Pinus radiata D. Don

Six sites with adult stands of P. Radiata representing the main soil groups in the VIII Region (soils derived from: granitic rock formed in situ, pleistocene volcanic ash, metamorphic schist rock, sea sediments, holocene volcanic ashes and andesitic-basaltic volcanic sands) were studied. Each site was characterised with respect to climate, chemical and physical properties of the soil, litter and aerial biomass of the forest. The inventory of nutrients (C, N, P, K) of the soil-litter-forest system was evaluated. Tree growth was related to site factors, and those limiting factors were identified in each case. Finally the main management measures for the sustainability of P. radiata plantations in each site were deduced.

Nitrogen Isotope Ratios in Sedimentary Organic Matter Track Changes in Nutrient Utilization and Inventories: ABSTRACT

The isotopic composition of sedimentary nitrogen is a direct proxy for the extent of nutrient draw-down in surface waters and for changes in nutrient inventories in past oceans. In the eastern Pacific, surface sediment [delta][sup 15]N is lowest along the equator where surface ocean nitrate concentration ([NO[sub 3]-]) is highest; [delta][sup 15]N progressively increases and [NO[sub 3]-] decreases to the north and south. This pattern is produced by the formation and sedimentation of [sup 14]N-enriched organic material (OM) where phytoplankton growth is not limited by NO[sub 3]-, and the formation of isotopically heavy OM where NO[sub 3]- is progressively drawn down. Downcore records from the Panama Basin and Northwest Africa show a 1 to 2% decrease in [delta][sup 15]N from the Holocene (0 to 12 ky BP) to the last glacial maximum (LGM, 12 to 24 ky BP) due to a decrease in relative NO[sub 3]-utilization (biological uptake relative to supply) and an increase in OM burial rate due to an increase in productivity. Off northwestern Mexico and in the Arabian Sea, extensive denitrification in intermediate waters causes [delta][sup 15]N-enrichment of the source NO[sub 3]-, so that modern sediment [delta][sup 15]N is high. During the LGM, however, [delta][sup 15]N decreased more » because productivity and the extent of denitrification both fell. Hence, the global ocean NO[sub 3]- inventory increased, possibly leading to higher global productivity which could have been responsible for the lower glacial atmospheric pCO[sub 2]. « less

Large changes in oceanic nutrient inventories from glacial to interglacial periods

CHANGES in ocean chemistry and circulation have been invoked to explain the lower atmospheric CO2 concentrations of glacial periods observed in ice-core records1. The processes that modulate these concentrations are not well understood, but an increase in the nutrient inventory of the ocean is one mechanism that could lower atmospheric CO2 levels by enhancing oceanic biological productivity and CO2 storage1-3. The oceanic concentrations of one such nutrient, nitrate, may be regulated by changes in the rate at which it is degraded by bacteria (denitrification) in oxygen-deficient subsurface waters. Denitrification constitutes a significant global sink for oceanic nitrate4, and the eastern tropical North Pacific Ocean is particularly important in this respect as it accounts for at least a third of global oceanic fixed-nitrogen removal by water-column denitrification4,5. Here we present 15N/14N records from marine sediment cores, which show that water-column denitrification in the eastern tropical North Pacific Ocean was greatly diminished during glacial periods. We suggest that, because nitrate limits biological productivity in much of the modern ocean, a consequent increase in the oceanic nitrate inventory during glacial periods could have contributed to the observed decrease in atmospheric CO2 concentration.

Coupled physical and biological modeling of the spring bloom in the North Atlantic (I): model formulation and one dimensional bloom processes

This is the first of two papers that introduce a mesoscale eddy resolving coupled physical and biological model system. The physical model consists of a quasigeostrophic interior with a fully coupled surface boundary layer. The nitrogen based biological model includes nitrate, phytoplankton, heterotroph and ammonium fields. This interdisciplinary model system is used to examine aspects of the 1989 JGOFS North Atlantic Bloom Experiment data set. This paper deals mainly with one dimensional processes and a companion paper addresses three dimensional phenomena. The data set consists of two time series of observations taken from different water masses in the mesoscale environment. The general features of the two time series are well represented by a one dimensional model when the mesoscale spatial variability in the initial condition is treated explicitly within the one dimensional framework. However, a significant bias is evident in the first time series as the sampling pattern began in a warm feature and moved toward colder ones. Mistaking spatial for temporal variability in this case results in an apparent sink of heat and source of nitrate in the data. Removing this bias with the one dimensional model results in an f-ratio that is almost a factor of two higher (0.64) than computed by other authors based on nutrient inventories and primary productivity measurements (0.37). The second time series was conducted in the interior of a mesoscale feature and spatial biasing is minimal. The model forms a seasonal thermocline and nitracline that compare quite well with the data in both magnitude and vertical extent. A subsurface ammonium maximum is generated by the model from an initially homogeneous profile that also agrees well with the data. Simulated primary productivity profiles match 14C incubations except on the final day of the simulation when surface nutrients appear in to have been exhausted slightly prematurely. Computed f-ratios are consistent with independent estimates based on uptake measurements. A systematic parameter dependence and sensitivity analysis is carried out on these results. The most sensitive parameters are the phytoplankton and heterotroph maximum growth rates. Detailed analysis of the behavior of the system indicates tight coupling between phytoplankton production and heterotrophic consumption even in the early stages of the bloom.

Reassessment of the oceanic residence time of phosphorus

Phosphorus (P) is an essential nutrient for the growth of all organisms and is believed to limit marine productivity, especially on geologic time scales (Holland, 1984; Smith, 1984; Howarth, 1988; Codispoti, 1989). As a result of the link between marine photosynthetic productivity and atmospheric CO2, phosphorus along with other nutrients present in short supply in the euphoric zone have been cited as potential players in the ocean's role in climate change. This link has been referred to as the nutrient-CO2 connection (Broecker, 1982). Model simulations which aim to quantify the role of oceanic nutrient inventories in promoting or enhancing climate change rely on the most currently formulated element budgets for the ocean. In this paper significant modifications to the currently accepted marine phosphorus budget are proposed. The modified P budget presented here requires a reassessment of phosphorus residence time in the ocean, and a concomitant review of the role of P as a potential player in climate change over glacialinterglacial time scales. Element budgets constructed for the oceans consist of a mass balance between inputs and outputs, for which the simplifying assumption is generally made that the ocean is in steady state with the specific element in question. The fluvial P flux constitutes the bulk of the input term for the marine phosphorus budget (atmospheric input is < 10% of the fluvial input: Froelich et al., 1982 ). Burial with sediments is the mechanism for ultimate removal of P from the oceans. For a system at steady state, the input flux equals the output flux. In the present paper, we focus on the output flux, burial with sediments, for two reasons. First, the chemistry of phosphorus buried in sediment cores, from which P burial fluxes are calculated, has not been affected to the same degree as rivers by anthropogenic perturbation. It is therefore simpler to quantify the output term of the P budget which can be extrapolated to pre-anthropogenic times. Second, detailed P speciation data permit us to quantify the burial flux of reactive-P as contrasted with refractory-P in sediments. This distinction is significant because burial of reactive-P constitutes removal of potentially bio-available P from the oceans. Two types of modification to the marine phosphorus budget are proposed here. First, the locus of P burial is addressed. Specifically, the importance of P burial in the deep sea is contrasted with P burial in continental margins. Second, the burial flux is characterized in terms of reactive(potentially bio-available) P vs. refractory-P. This distinction is made possible by obtaining detailed P speciation data from application of the SEDEX method (Ruttenberg, 1992), a selective leaching procedure which separates solid-phase P into five reservoirs on the basis of chemical reactivity: loosely-sorbed P; ferric iron bound-P; authigenic apatite + biogenic apatite + C a C O 3 bound-P; detrital apatite P; and organic-P. Detailed P spe-

The carbon balance during the 1989 spring bloom in the North Atlantic Ocean, 47°N, 20°W

We report on studies of the carbon balance of the upper water column, done as part of the JGOFS North Atlantic Bloom Experiment, over a 13-day period, at 47°N, 20°W, during the 1989 spring phytoplankton bloom. Gross carbon production was calculated from data on 18O gross O 2 production and from 14C production as well. Net carbon production was calculated from net O 2 production rates measured in vitro, as well as from changes in the inventories of nutrients and O 2 along with O 2 evasion rates by gas exchange. Gross carbon production during this period was measured to be 1.83 mol m −2, and net production was 0.68 mol m −2. Of this net carbon production, 0.30 mol m −2 was stored in the euphotic zone as particulate organic carbon, and 0.09 mol m −2 rained out to depths >150 m. The remainder was remineralized to DIC in the 50–150 m depth interval, with perhaps some DOC storage in the upper 150 m.

Comparison of Tropical Tree Plantations with Secondary Forests of Similar Age

The structure and dynamics of small plantations of pine (Pinus caribaea; 4 and 18.5 yr old in 1980) and mahogany (Swietenia macrophylla; 17 and 49 yr old in 1980) were compared with those of paired secondary forest stands of similar age and growing adjacent to each other under similar edaphic and climatic conditions. The study was conducted in the Luquillo Experimental Forest between 1980 and 1984. Comparisons included a variety of demographic, production, and nutrient cycling characteristics of stands. Although the small unmanaged plantations had a lower number of species in understory than paired secondary forests, the understory of the older plantations developed high species richness, including many of native tree species. After 17 yr, native tree species invaded the overstory of plantations. After 50 years the species richness in the understory of a mahogany plantation approached that of its paired secondary forest. Plantation understories had important ecological roles, including high nutrient accumulation. Understory plant tissue, particularly leaf litter, had higher nutrient concentration in pine plantations than in paired secondary forests. Understory biomass in plantations accumulated a higher proportion of the total nutrient inventory in the stand than did the understory in paired secondary forests. Plantations had higher aboveground biomass and net aboveground biomass production than paired secondary forests. Higher root densities and biomass were found in secondary forests as were greater depth of root penetration, higher nutrient concentration in roots, and more microsites where roots grow, than paired plantations. These characteristics may improve the capacity of secondary forests relative to that of paired plantations to rapidly recapture nutrients that become available by mineralization and that could otherwise be lost through hydrological or gaseous pathways. Both forest types accumulated nutrients and mass, but secondary forests recirculated nutrients much faster than the plantations, which tended to store the nutrients. Plantations had higher leaf fall and total litterfall, had litterfall with lower nutrient concentrations, accumulated more nutrients in litter, decomposed more litter on an annual basis, exhibited more variation in the spatial distribution of litter mass, and had more month—to—month variation in litter storage than paired secondary forests. Litter of the secondary forests, on the other hand, had a faster nutrient turnover than plantation litter, though plantations retranslocated more nutrients before leaf fall than did secondary forests. Nutrient retranslocation increased with plantation age. Plantations, particularly pine plantations, produced more litter mass per unit nutrient return than did paired secondary forests. Total nutrient storage in soil gave the best correlation with nutrient use efficiency estimated as element: mass ratios in various compartments. Nutrient use efficiency ranked differently among forest pairs, depending upon which nutrient and ecosystem parameters were being compared. Because of high retranslocation of nutrients, and in spite of greater nutrient "need" to produce higher biomass, plantations had nutrient demands on soil similar to paired secondary forests. Among the ecosystem parameters measured, nutrients in leaf fall correlated best with differences in soil nutrients across stands. Nutrient concentrations in understory species appeared to be a sensitive indicator of whole—stand nutrient use efficiency. Some of the observations of the study could be attributed to intrinsic differences between small unmanaged plantations and secondary forests, but many could be explained by species differences (i.e., timing of leaf fall), age of plantation (i.e., accumulation of biomass or species), or the relative importance of angiosperms and gymnosperms (i.e., nutritional quality of litter). The study challenges the conventional dogma with respect to differences between plantations and native successional ecosystems and underscores the dangers of generalizing about all tropical tree plantations or all natural tropical forests, or even extrapolating from one sector of the ecosystem to another.

Nitrogen accumulation in a chronosequence of red alder communities along the Hoh River, Olympic National Park, Washington

Alnusrubra Bong, dominates the first 65 – 80 years of a sere that is initiated naturally on the terraces of the Hoh River. Stands of 14, 24, and 65 years were studied to determine to what extent the Alnus stage enriched the nitrogen inventory of the site. Bare sandbars deposited by the river had a mean of 783 kg/ha nitrogen. Alnus communities caused an increase in the nitrogen inventory so that, by 65 years, total community nitrogen was 4659 kg/ha, soils held 3594 kg/ha N in the upper 45 cm, and Alnus trees held 942 kg/ha N. The nitrogen contents of the soil, Alnus wood, bark, and branches, grasses, total aboveground biomass, total belowground biomass, and sticks less than 1 cm diameter all showed significant increases from 14 to 65 years. The A. rubra stage is an important link in the nutrient inventory between unvegetated, recently deposited sandbars and the climax coniferous forests dominated by Tsugaheterophylla (Raf.) Sarg. and Piceasitchensis (Bong.) Carr.

Symposium on Pasture Methods for Maximum Production in Beef Cattle: Manipulation of Both Livestock and Forage Management to Give Optimum Production

Optimum range livestock production can be achieved only through compatible livestock and forage management. The first requirement in developing a range livestock and forage management program is a quantitative and qualitative inventory of forage resources. This means an inventory of range forage nutrients at specific times during the grazing season. Only after the relative seasonal availability of nutrients is known, can livestock be managed to obtain a maximum return from the available forage resources. Research reported herein was conducted on an eastern Oregon sagebrush-bunchgrass area, the Squaw Butte Experiment Station. The area with a mean elevation of 1,375 m annually averages about 30 cm precipitation, two-thirds of which occurs as snow in winter and the remainder as rain during the growing season of April, May and June. Research involves not only native vegetation but also introduced species, primarily crested wheat-grass (Agropyron desertorum). These studies are mainly concerned with the management of both range and livestock during the spring, summer and fall.

Nutrition Research: Some Problems of the Total Tree Approach

AbstractTotal tree analysis can yield an inventory of nutrients within a stand and, indirectly, a measure of nutrient uptake. The latter may be obtained more accurately by a combination of methods. Stand weight is best estimated by relating tree size to weight from large, intermediate, and small trees. Accurate estimation of nutrient concentrations requires sampling from additional size classes. Attempts to sample average trees yield biased estimates. The number of sample trees required per stand varies with stand characteristics. Five trees per plot gave average prediction errors between 7 and 23% for different parts of red pine trees. To be commensurate with the field work required, laboratory techniques should be of high quality and include analysis for a wide range of elements. Although too cumbersome for a diagnostic tool and, probably, too damaging for use in most permanent sample plots this technique can yield much basic information on stand nutrition and related problems.