Community collocation of four submerged macrophytes on two kinds of sediments in Lake Taihu, China

To explore a method for rapid restoration and artificial regulation of submerged macrophytes in large-scale restoration of eutrophic lakes, the succession and the biodiversity changes of four communities composed of four native, common submerged macrophytes, Hydrilla verticillata, Potamogeton malaianus, Vallisneria spiralis and Najas marina, on two kinds of sediments were investigated. Under low light intensity (reduced by 99%), the plant biomass changed with seasonal changes, plant competition, and environmental stress. The competitive capability for light differed in the four species due to different shoot height and tiller number. After 405 days of transplantation, H. verticillata became dominant in all communities. The biomass of H. verticillata, with strong ability to endure low water light environment, accounted for more than 90% of the total community biomass, and P. malaianus had only weak growth, while V. spiralis and N. marina almost disappeared. Based on livability and biomass of submerged macrophytes on two sediment types, brown clay sediment appeared to be more favorable for the settlement of the plants, while fertile sludge sediment was suitable for vegetative growth. In conclusion, the improvement of habitats and the selection of appropriate plant species are of the greatest importance for ecological restoration of the aquatic ecosystem.     

Effects of the density of the invasive macrophyte <Emphasis Type="Italic">Hydrilla verticillata</Emphasis> and root competition on growth of one native macrophyte in different sediment fertilities

The occurrence of non-native species at high densities may generate competition for resources and possibly exclude native species in various environments. We evaluated the effects of increased densities of the non-native invasive macrophyte Hydrilla verticillata on the growth of the native species Egeria najas in different sediment types and with only root interactions or root?+?shoot interactions. We tested the hypothesis that the effect of the invasive on the native species is density dependent and that it is greater when competition for light and nutrients occurs (root?+?shoot interactions). The results of these experiments demonstrated that increased density of the invasive species H. verticillata significantly decreased the growth of the native species independent of sediment type (sand or mud sediments). When plants competed for water and sediment resources (root?+?shoot interactions), the native species was more impacted by the invasive than when they competed only for water resources (only shoots interacting). Our results show that E. najas is probably unable to colonize sites highly colonized by hydrilla, and this applies to both sand and mud sediments. This outcome suggests that H. verticillata is a threat for E. najas and likely other native submerged species in South America.     

Impacts of sediment type on the performance and composition of submerged macrophyte communities

To restore deteriorated lake ecosystems, it is important to identify environmental factors that influence submerged macrophyte communities. While sediment is a critical environmental factor for submerged macrophytes and many studies have examined effects of sediment type on the growth of individual submerged macrophytes, very few have tested how sediment type affects the growth and species composition of submerged macrophyte communities. We constructed submerged macrophyte communities containing four co-occurring submerged macrophytes (Hydrilla verticillata, Myriophyllum spicatum, Ceratophyllum demersum and Chara fragilis) and subjected them to three sediment treatments, i.e., clay, a mixture of clay and quartz sand at a volume ratio of 1:1 and a mixture at a volume ratio of 1:4. Compared to the clay, the 1:1 mixture treatment greatly increased overall biomass, number of shoot nodes and shoot length of the community, but decreased its diversity. This was because it substantially promoted the growth of H. verticillata within the community, making it the most abundant species in the mixture sediment, but decreased that of M. spicatum and C. demersum. The sediment type had no significant effects on the growth of C. fragilis. As a primary nutrient source for plant growth, sediment type can have differential effects on various submerged macrophyte species and 1:1 mixture treatment could enhance the performance of the communities, increasing the overall biomass, number of shoot nodes and shoot length by 39.03%, 150.13% and 9.94%, respectively, compared to the clay treatment. Thus, measures should be taken to mediate the sediment condition to restore submerged macrophyte communities with different dominant species.     

Response of Potamogeton crispus root characteristics to sediment heterogeneity

Plant growth, biomass allocation, root distribution and plant nutrient content were investigated in the submerged macrophyte Potamogeton crispus growing in heterogeneous sediments. Three experimental sediments heterogeneous in nutrient content and phosphorus release capacity were used: sandy loam with low nutrient content (A), clay with intermediate nutrient content (B), and clay with high nutrient content (C). Biomass accumulation was significantly affected by the sediment type, and was highest in clay C (1.23 mg per plant dry weight) but lowest in sandy loam (0.69 mg per plant dry weight). The root:shoot ratios in treatments A, B and C were 0.30, 0.14 and 0.09, respectively. P. crispus allocated more biomass to roots in sandy loam compared with the other sediments. The average root numbers in sediments A, B and C were 16, 19 and 20, respectively, and the total root lengths in sediments A, B and C were 238.84, 200.36 and 187.21 cm, respectively. Almost 90% of the root biomass was distributed in the 0–15 cm depth in sediments B and C, compared with 64.53% in sediment A. The rank order of plant nitrogen and phosphorus concentrations in the sediment types was C > B > A. These results indicate that both sediment structure and nutrient availability influence the growth and distribution of the root system of P. crispus.     

Species and Biogeochemical Cycles of Organic Phosphorus in Sediments From a River With Different Aquatic Plants Located in Huaihe River Watershed,China

The results of phosphorus fractionation in the sediments from a contaminated river containing different aquatic plants, analyzed by solution ³¹P-NMR for Organic Phosphorus, showed that the concentration of Inorganic Phosphorus dominated in all species and Organic Phosphorus accounted for over 20% of Total Phosphorus. In general, orthophosphate was dominant in all the sampling sites. The proportion of Organic Phosphorus accounting for the Total Phosphorus in the sediments with different plant decreased in the following order: Paspalum distichum > Typha orientalis > Hydrilla verticillata. Phosphorus-accumulation ability of Paspalum distichum was obviously stronger than Typha orientalis and Hydrilla verticillata. The Organic Phosphorus was in aquatic plants dominated by humic-associated P (Hu-P), which converted to Inorganic Ohosphorus more significantly in submerged plants than in emerged plants. The sediment dominated by Paspalum distichum abundantly accumulated Organic Phosphorus in the orthophosphate monoester fraction. The degradation and mineralization of orthophosphate monoester was the important source of high Inorganic Phosphorus concentration and net primary productivity in Suoxu River. The Organic Phosphorus derived from Typha orientalis and Hydrilla verticillata was dramatically converted to Inorganic Phosphorus when the environmental factors varied.     

Experiment of emergent macrophytes growing in contaminated sludge: Implication for sediment purification and lake restoration

Three emergent macrophytes (Zizania latifolia (Turcz) Hand.-Mazz., Phragmites australis (Cav.) Trin. ex Steud. and Typha angustifolia Linn.) and three different sediments from Lake Dianchi of Yunnan province, China, were studied through orthogonal pot-planting experiment in order to compare the ability of the three emergent macrophytes in dealing with the contaminated sludge and to evaluate the possibility of purifying the sediment through aquatic plant rehabilitation. The results show that the number of sprouts and biomass of all the species growing in the sediment of site 3 were higher than those growing in the sediment of sites 1 and 2; the plants growing in the sediment of site 3 also exhibited the highest root activities; in each sediment, the sequence of root activity of the species was: Z. latifolia > P. australi > T. angustifolia; TP content in the sediments grown with different plants reduced significantly than those of control. These results indicated that these emergent plants were able to grow well in the contaminated sediment though it is black with a strong odor. Z. latifolia shows the highest root activity in the sediment of site 3, from which we can deduce that this plant should be the preferred pioneer species for purifying the sediment. According to their biomass and TN content and TP content, Z. latifolia, P. australi and T. angustifolia retained TN 16.6, 29.8, 12.8, and TP 2.2, 3.6, 3.9 g m^?2, respectively. Based on the climate of Dianchi valley, these plants can be harvested twice in a year. Thus, the amount of nutrient can be removed almost doubly. Therefore, the sludge can be purified through macrophytes restoration and not through sediment dredging, which was proved to be expensive and invalid in the large shallow lakes.     

Competition between two invasive Hydrocharitaceae (Hydrilla verticillata (L.f.) (Royle) and Egeria densa (Planch)) as influenced by sediment fertility and season

Competition between two invasive plants of similar growth form, Hydrilla verticillata (L.f.) (Royle) and Egeria densa (Planch), was studied in response to season and sediment fertility. These two invasive species were grown in outdoor concrete tanks in monocultures and mixtures. Five fertilization rates were tested for monocultures and two for mixtures where six combinations of planting densities were used in two seasons (spring and fall). Monitoring of plant biomass was made at the end of each of these 2-month-experiments. In contrast to E. densa, clear seasonal patterns in biomass production and in reproductive allocations of H. verticillata were evident. Competitive pressure for both species was lower during the fall experiment. Biomass production increased with fertilization for H. verticillata in monocultures and changes either in allocative ratios or in tuber production patterns were shown in response to nutrient availability. However, E. densa growth was not affected by fertilization. In most cases, H. verticillata was a better competitor than E. densa except when sediment was pure sand. Competition occurred mainly for nutrient uptake rather than for light harvesting. These results suggest that despite the similar ecology, H. verticillata may outcompete E. densa in many situations, probably due to its higher plasticity.     

Chemical characterization of the lipophilic extract of Hydrilla verticillata: a widely spread aquatic weed

The composition of the lipophilic extract from Hydrilla verticillata, the common aquatic weed collected from Sasthamkotta Lake, the largest freshwater lake in Kerala, south of the west coast of India, was investigated. The lake is a designated wetland of international importance under the Ramsar Convention since 2002. GC-MS study of the unsaponifiable lipophilic extract of H. verticillata confirmed the presence of 3,5,11,15-tetramethyl 1- hexadecen-3-ol (C₂₀H₄₀O) and phytol (C₂₀H₄₀O) as major components, and their structures were elucidated. Phytol and 3,5,11,15-tetramethyl 1- hexadecen3-ol are the two isomers of the diterpeneol (C₂₀H₄₀O) found in the unsaponifible lipophilic extract of H. verticillata and are formed by the hydrolysis of the alcohol moiety of chlorophyll. On quantification, an appreciable concentration of phytol (6.39 g?Kg^?1) was estimated. The feasibility to utilize H. verticillata to produce phytol is to be addressed by further studies since H. verticillata is considered as one of the world’s fast widely spread aquatic weeds on account of its numerous mechanisms of vegetative reproductions.     

Effects of pH on the Submerged Macrophyte <Emphasis Type="Italic">Hydrilla verticillata</Emphasis>

Hydrilla verticillata (L.f.) Royle is widely distributed and protects the water environment mainly by serving as a potential heavy metal hyperaccumulator. Hydroponic experiments were performed to investigate the biochemical responses of the leaves and stems of H. verticillata at pH values of 5.5, 6.5, 7.5, 8.5, and 9.5 for 7, 14, and 21 days. The results showed that a weak alkaline environment (pH 8.5) promoted plant growth and that an acidic environment (pH 5.5, 6.5) adversely affected normal metabolism. The malondialdehyde content and three antioxidant enzyme activities changed in a similar pattern after the pH treatments: varying increases occurred following all pH treatments with the exception of pH 8.5. The activities of the three N metabolism enzymes briefly increased in an acidic environment and then sharply decreased compared to the control. The ROS-scavenging mechanisms and N metabolism mechanisms in H. verticillata worked together to respond to pH-induced effects. Based on the interplay between antioxidant enzymes and N metabolism enzymes, H. verticillata could defend against the toxicity induced by an acidic environment for approximately seven days and demonstrate stronger adaptability to the alkaline environment. Depending on the growth status and the synergistic effects of the enzymes, an optimum pH of 8.5 for H. verticillata was found in our experiment. Thus, these characteristics reveal a better understanding of this species so that it can be effectively controlled and better referenced for phytoremediation.     

Colonization dynamics of ciliate morphotypes modified by shifting sandy sediments

Sandy stream-bed sediments colonized by a diverse ciliate community are subject to various disturbance regimes. In microcosms, we investigated the effect of sediment shifting on the colonization dynamics of 3 ciliate morphotypes differing in morphology, behavior and feeding strategy. The dynamics of the ciliate morphotypes inhabiting sediment pore water and overlying water were observed at 3 sediment shifting frequencies: (1) stable sediments, (2) periodically shifting sediments such as migrating ripples, and (3) continuously shifting sediments as occurring during scour events of the uppermost sediment. Sediment shifting significantly affected the abundance and growth rate of the ciliate morphotypes. The free-swimming filter feeder Dexiostoma campylum was vulnerable to washout by sediment shifting since significantly higher numbers occurred in the overlying water than in pore water. Abundance of D. campylum only increased in pore water of stable sediments. On the contrary, the vagile grasper feeder Chilodonella uncinata and the sessile filter feeder Vorticella convallaria had positive growth rates and successfully colonized sediments that shifted periodically and continuously. Thus, the spatio-temporal pattern of sediment dynamics acts as an essential factor of impact on the structure, distribution and function of ciliate communities in sand-bed streams.     

Growth,biomass allocation,and autofragmentation responses to root and shoot competition in Myriophyllum spicatum as a function of sediment nutrient supply

Plant growth, biomass allocation and autofragmentation were investigated in response to root and shoot competition in the submersed macrophyte Myriophyllum spicatum L. growing in two sediment environments. Biomass accumulation and allocation were significantly affected by sediment fertility, with a higher total biomass observed in fertile sediment (average: 4.69 g per plant vs. 1.12 g per plant in infertile sediment). Root-to-shoot ratios were 0.34 and 0.06 in the infertile and fertile sediments, respectively, reflecting the high investment placed on roots under infertile conditions. In the presence of root, shoot, and full competition, whole plant biomass decreased by 18%, 12% and 24% in the infertile sediments, and 23%, 25% and 33% in the fertile sediments, respectively. Root weight ratios (RWRs) increased with root competition by 38% (P < 0.001) and 12% (P = 0.002), while leaf weight ratios (LWRs) decreased with shoot competition by 6% (P = 0.042) and 5% (P = 0.001) in the infertile and fertile sediments, respectively. A total of 406 autofragments were harvested in the fertile sediments, but none were obtained from the infertile sediments. In the control, autofragment number and biomass was 166% and 175% higher compared to the competition treatment. Root and shoot competition resulted in a 21% (P = 0.043) and 18% (P = 0.098) decrease in the autofragment biomass, respectively. These results indicated that M. spicatum responds to different sediment fertility by changing its allocation patterns. Moreover, both root and shoot competition influenced plant growth and autofragmentation, while sediment nutrient availability played an important role in M. spicatum autofragmentation.     

Growth of Hydrilla verticillata (L.f.) Royle under controlled conditions

Aquatic macrophytes are important resources for the maintenance of trophic chains and in biogeochemical processes, but they can also be deleterious for several uses if present in excess. Hydrilla verticillata was found in the Paraná River (Brazil) after 2005, which requires monitoring owing to the invasive potential of this species. In this study, we measured the growth of H. verticillata under controlled conditions and compared the growth dynamics for the two development strategies (branch and tuber). We show that this species has great potential to develop in tropical (Brazilian) aquatic ecosystems. The parameters from the modelling of the growth kinetics indicated a doubling time of 19.8 days for H. verticillata growing from stems; however, the growth from tubers were much faster, with doubling times ranging from 2.5 to 11 days. The delay for the tubers to sprout caused a decrease in the number of branches of H. verticillata stems. From the growth parameters obtained from the experiments under controlled conditions, we concluded that the high temperature and light availability in most South American reservoirs (including the Porto Primavera Reservoir where it was first recorded) are suitable for H. verticillata to compete and probably displace other native aquatic macrophytes, such as Egeria najas, Egeria densa, and Cerathophyllum demersum. This is a matter of concern because these and other submersed species are commonly found in several natural and man-made South-American aquatic ecosystems, where they are key for biodiversity maintenance.     

The relationships between relative growth rate,meristematic potential and compensatory growth of semiarid-land shrubs

The submersed macrophyte Vallisneria americana was grown for seven weeks in a greenhouse to test for differences in the ability of three different sediments to support growth stimulation in response to CO₂ enrichment at low pH. Plants accumulated 21- to 24-fold greater biomass at 10 × ambient CO₂ concentrations than at ambient CO₂ on all sediments. At both CO₂ levels, plants grown on sediment from an acidified lake accumulated ca. 81%, and those grown on oligotrophic lake sediment ca. 47% as much biomass as plants grown on alkaline lake sediment. Despite striking CO₂ and sediment effects on biomass accumulation, there was no significant interaction (using log-transformed data) between CO₂ and sediment effects, indicating that all sediments allowed similar proportionate growth responses to CO₂ enrichment. Plants grown on the less fertile sediments showed greater relative allocation to horizontal versus vertical growth by producing more rosette-bearing stolons in relation to plant height (leaf length) than plants grown on relatively fertile, alkaline lake sediment. Tissue analysis suggested that sediment effects on Vallisneria growth could be attributed neither to mineral putrient (nitrogen and phosphorus) limitation nor to aluminum toxicity in these low pH treatments. In any case, CO₂ availability can be an important regulator of submersed macrophyte growth at low pH on a variety of sediment types, including those from oligotrophic and acidic lakes.     

The relative importance of sediment and water column supplies of nutrients to the growth and tissue nutrient content of the green macroalga Enteromorpha intestinalis along an estuarine resource gradient

Large blooms of opportunistic green macroalgae such as Enteromorpha intestinalis are of ecological concern in estuaries worldwide. Macroalgae derive their nutrients from the water column but estuarine sediments may also be an important nutrient source. We hypothesized that the importance of these nutrient sources to E. intestinalis varies along a nutrient-resource gradient within an estuary. We tested this in experimental units constructed with water and sediments collected from 3 sites in Upper Newport Bay estuary, California, US, that varied greatly in water column nutrient concentrations. For each site there were three treatments: sediments + water; sediments + water + Enteromorpha intestinalis (algae); inert sand + water + algae. Water in units was exchanged weekly simulating low turnover characteristic of poorly flushed estuaries. The importance of the water column versus sediments as a source of nutrients to E. intestinalis varied with the magnitude of the different sources. When initial water column levels of dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) were low, estuarine sediments increased E. intestinalis growth and tissue nutrient content. In experimental units from sites where initial water column DIN was high, there was no effect of estuarine sediments on E. intestinalis growth or tissue N content. Salinity, however, was low in these units and may have inhibited growth. E. intestinalis growth and tissue P content were highest in units from the site with highest initial sediment nutrient content. Water column DIN was depleted each week of the experiment. Thus, the water column was a primary source of nutrients to the algae when water column nutrient supply was high, and the sediments supplemented nutrient supply to the algae when water column nutrient sources were low. Depletion of water column DIN in sediment + water units indicated that the sediments may have acted as a nutrient sink in the absence of macroalgae. Our data provide direct experimental evidence that macroalgae utilize and ecologically benefit from nutrients stored in estuarine sediments.     

Resource allocation in the submerged plant Vallisneria natans related to sediment type, rather than water-column nutrients

1. Phenotypic plasticity in resource allocation by Vallisneria natans was investigated in a greenhouse experiment, using three types of sediment [sandy loam, clay, and a 50 : 50 (by volume) mixture of the two sediments] and two levels of water‐column nutrient. The clay was collected from a highly eutrophic lake in Jiangsu Province, China, and the N and P concentrations applied in nutrient media were at the upper limits observed in most lakes of China. 2. Growth and biomass allocation were significantly affected by sediment type, rather than water‐column nutrients. Plant growth in clay and the mixture were similar, and 2.4–3.4 times higher than that in sandy loam. Compared with the plants grown in clay or the mixed sediments, the plants grown in sandy loam allocated relatively more biomass to root (11–17% versus 7–8% of total biomass), and relatively less to leaf (76–82% versus 86–87% of total biomass). Plastic variations in root area were induced by sediment type alone (P < 0.05), whereas the impacts of sediment type and water‐column nutrients on leaf area were insignificant (P > 0.05). 3. Plant N and P concentrations were significantly affected by both sediment type and water‐column nutrients. Increased nutrient availability in the water column enhanced plant N concentration by 3.5–20.2%, and plant P concentration by 19.1–25.8%. 4. Biomass accumulation and plant nutrient concentration in plants grown in different sediment types and water‐column nutrients indicate that sediment type had more significant impacts on growth and N and P concentrations of V. natans than did water‐column nutrients. Changes in phenotype are a functional response to nutrient availability in sediment, rather than to water‐column nutrients.     

杭州湾滨海湿地不同植被类型沉积物磷形态变化特征

研究了杭州湾滨海湿地不同植被类型下0-5 cm和10-20 cm沉积物总磷(TP)、无机磷(IP)、有机磷(OP)及其形态变化特征,揭示湿地植被演替对沉积物磷形态的影响.结果表明,沉积物TP,互花米草(MC)显著高于其他植被类型.在IP中,可溶性松散态磷(Soluble and loosely bound P,SL-Pi)含量光滩(CK)最小、MC最大;还原态可溶性磷(Reductant soluble P,RS-Pi)含量芦苇(LW)和MC显著高于CK和海三棱藤草(BC);钙磷(Ca-Pi)含量CK和BC显著大于LW和MC.在OP中,活性有机磷( Labile Po,L-Po)含量最低、中等活性有机磷(Moderately labile Po,ML-Po)含量最高、非活性有机磷(Nonlabile Po,NL-Po)处于中间水平.IP是磷素的主要形态、占TP的74％ -89％,而Ca-Pi又是IP的主要形态、于湿地沉积物淤积初期通过吸附沉淀作用存留.杭州湾湿地植被自然演替过程中不同植物生物量积累和营养物质循环过程的变化导致沉积物中磷形态的差异.植被演替初期,BC显著改变0-5 cm沉积物磷形态,对10-20 cm沉积物无显著影响;植物演替后期的LW和MC促使0-5 cm沉积物有机磷快速积累、10-20 cm沉积物有机磷小幅增加,同时促进Ca-Pi向可溶性、活性态磷转变.     

Gene Transfer in Marine Water Column and Sediment Microcosms by Natural Plasmid Transformation

We investigated the possibility for natural transformation in the marine environment by using broad-host-range plasmid multimers and a high-frequency-of-transformation (HFT) Vibrio strain as the recipient. Water and sediment samples were taken from Tampa Bay, the eastern Gulf of Mexico, the Florida Shelf near Miami, and the Bahamas Bank. In water column microcosms, transformation frequencies ranged from 1.7 × 10^-6 to 2.7 × 10^-10 transformants per recipient, with highest frequencies occurring when low levels of nutrients (peptone and yeast extract) were added. The presence of the ambient community either reduced transformation frequency by an order of magnitude or had no effect. In sterile sediments, nutrient additions had no consistent effect on transformation, with transfer frequencies similar to those observed in the water column. Transformation was not observed in any sediment experiment when the ambient microbial community was present. These findings are the first report of natural plasmid transformation in seawater and in the presence of the ambient microbial community. This process may be a mechanism for the acquisition of small, nonconjugative plasmids, which are commonly found in aquatic bacteria. Our data also suggest that natural transformation may be more likely to occur in the water column than in native marine sediments, contradicting prior conclusions based on studies with sterile sediments.     

Aquatic vegetation and trophic condition of Cape Cod (Massachusetts,U.S.A.) kettle ponds

The species composition and relative abundance of aquatic macrophytes was evaluated in five Cape Cod, Massachusetts, freshwater kettle ponds, representing a range of trophic conditions from oligotrophic to eutrophic. At each pond, aquatic vegetation and environmental variables (slope, water depth, sediment bulk density, sediment grain size, sediment organic content and porewater inorganic nutrients) were measured along five transects extending perpendicular to the shoreline from the upland border into the pond. Based on a variety of multivariate methods, including Detrended Correspondence Analysis (DCA), an indirect gradient analysis technique, and Canonical Correspondence Analysis (CCA), a direct gradient approach, it was determined that the eutrophic Herring Pond was dominated by floating aquatic vegetation (Brasenia schreberi, Nymphoides cordata, Nymphaea odorata), and the algal stonewort, Nitella. Partial CCA suggested that high porewater PO₄-P concentrations and fine-grained sediments strongly influenced the vegetation of this eutrophic pond. In contrast, vegetation of the oligotrophic Duck Pond was sparse, contained no floating aquatics, and was dominated by emergent plants. Low porewater nutrients, low sediment organic content, high water clarity and low pH (4.8) best defined the environmental characteristics of this oligotrophic pond. Gull Pond, with inorganic nitrogen-enriched sediments, also exhibited a flora quite different from the oligotrophic Duck Pond. The species composition and relative abundance of aquatic macrophytes provide good indicators of the trophic status of freshwater ponds and should be incorporated into long-term monitoring programs aimed at detecting responses to anthropogenically-derived nutrient loading.     

Growth,biomass allocation,and autofragmentation responses to root and shoot competition in Myriophyllum spicatum as a function of sediment nutrient supply

Plant growth, biomass allocation and autofragmentation were investigated in response to root and shoot competition in the submersed macrophyte Myriophyllum spicatum L. growing in two sediment environments. Biomass accumulation and allocation were significantly affected by sediment fertility, with a higher total biomass observed in fertile sediment (average: 4.69 g per plant vs. 1.12 g per plant in infertile sediment). Root-to-shoot ratios were 0.34 and 0.06 in the infertile and fertile sediments, respectively, reflecting the high investment placed on roots under infertile conditions. In the presence of root, shoot, and full competition, whole plant biomass decreased by 18%, 12% and 24% in the infertile sediments, and 23%, 25% and 33% in the fertile sediments, respectively. Root weight ratios (RWRs) increased with root competition by 38% (P < 0.001) and 12% (P = 0.002), while leaf weight ratios (LWRs) decreased with shoot competition by 6% (P = 0.042) and 5% (P = 0.001) in the infertile and fertile sediments, respectively. A total of 406 autofragments were harvested in the fertile sediments, but none were obtained from the infertile sediments. In the control, autofragment number and biomass was 166% and 175% higher compared to the competition treatment. Root and shoot competition resulted in a 21% (P = 0.043) and 18% (P = 0.098) decrease in the autofragment biomass, respectively. These results indicated that M. spicatum responds to different sediment fertility by changing its allocation patterns. Moreover, both root and shoot competition influenced plant growth and autofragmentation, while sediment nutrient availability played an important role in M. spicatum autofragmentation.     

Agar Sediment Test for Assessing the Suitability of Organic Waste Streams for Recovering Nutrients by the Aquatic Worm Lumbriculus variegatus

An agar sediment test was developed to evaluate the suitability of organic waste streams from the food industry for recovering nutrients by the aquatic worm Lumbriculus variegatus (Lv). The effects of agar gel, sand, and food quantities in the sediment test on worm growth, reproduction, and water quality were studied. Agar gel addition ameliorated growth conditions by reducing food hydrolysis and altering sediment structure. Best results for combined reproduction and growth were obtained with 0.6% agar-gel (20 ml), 10 g. fine sand, 40 g. coarse sand, and 105 mg fish food (Tetramin). With agar gel, ingestion and growth is more the result of addition of food in its original quality. Final tests with secondary potato starch sludge and wheat bran demonstrated that this test is appropriate for the comparison of solid feedstuffs and suspended organic waste streams. This test method is expected to be suitable for organic waste studies using other sediment dwelling invertebrates.