Pelham Bay Park, the largest municipal park in the New York City, is located on Long Island Sound, in the northeastern corner of the Borough of the Bronx. It contains nearly 500 acres of tidal marshes [20] (NYS DOS, 1992), comprised of high marshes, intertidal marshes, salt flats, lagoons, a narrow bay, and a wetland complex. The area is managed by the City of New York Department of Parks and Recreation [20] (NYS DOS, 1992). Wetland and aquatic habitats in Pelham Bay Park have been seriously degraded by discharges of sewage, stormwater runoff, and industrial effluents containing heavy loads of nutrients, sediments, or chemical pollutants into contiguous water bodies; or water pollution caused by oil spills, waste disposal, and excessive turbidity causing by construction/dredging [20] (NYS DOS, 1992).

The Pelham Bay wetlands are located in Pelham Bay Park, Bronx, NY. The Pelham Bay Park Wetlands, one of the largest natural estuarine habitats on the north shore of western Long Island Sound, is the only undisturbed tidal wetlands areas remaining in the Bronx [20] (NY DOS, 1992). For this study we collected samples at six sampling sites within the wetlands area. The six fresh water wetland sites locations were (Figure 1; Table 1): sites 1, 2, 3, and 4, located in the

wetlands close to the Bartow-Pell Mansion Museum; site 5 in the wetland at the Pelham Golf Course; and site 6 located in a ditch in the Split Rock Golf Course (Figure 1). The major contents in the sediment are silt and clay. The sediment at sites 1, 2, and 3 were very sticky and silty; site 4 was more sandy, with detritus materials such as plant roots; sites 5 and 6 had a putrid smell, very sticky, composed mostly of silt and clay. The putrid odor came from fertilizer that had applied on the golf courses.

Sediment samples were collected from the six wetland sites in July 2006. Each site was located with a Global Positioning System (GPS) unit, and the coordinates are provided in Table 1. A Core Sampler (diameter = 8 cm; length = 17 cm) was used to obtain the bed sediments. The sediment samples were sealed in one gallon zipper bags, and transported to the Environmental Laboratory of the Department of Environmental, Geographic, and Geological Sciences, Lehman College of The City University of New York at the end of each sampling day, and stored at 4˚C until further experimentation. The sediment samples were immediately homogenized and saved in waterproof double-track zipper bags (10.2 × 15.2 cm; made by Fisher Scientific Co., USA), and stored at 4˚C until they were used for further analysis. A portion of each homogenized sediment sample was dried at 70˚C for 72 h, and then finely ground and used for selected physico-chemical analysis.

The wet sediment samples were oven dried at 105˚C for 24 h and then analyzed for their water content; sediment samples were also dried at 70˚C for 72 h and finely ground for total phosphorus (TP) analysis. To determine TP, 0.5 to 1.0 g of finely ground dry sediments were combusted at 550˚C in a muffle furnace for 5 h and the ash was dissolved in 6 M HCl. The digestate was filtered to a 100 ml volumetric flask with Fisher filter paper using an automated ascorbic acid method (ESS Method 310.1; USEPA, 1992) [21]. Meanwhile, the total organic matter (TOM) in sediments was determined by combustion in a muffle furnace. The total organic carbon (TOC) is equal to 0.58 times of the amount of TOM (TOC = 0.58*TOM).

To determine the different poorly crystalline Fe and Al effect on phosphorus sorption, 0.5 g of finely ground dry sediment was extracted with 30 ml 0.175 M ammonium oxalate + 0.1 M oxalic acid at a ratio of 1:60 (0.5 ml/30ml = 1:60) by shaking for 4 h on an end-over-end mechanical shaker [22] (Pant and Reddy, 2001). Then the suspensions were centrifuged at 10,000 rpm for 10 min and filtered through a 0.45 µm membrane filter in the dark. The filtrates were analyzed for oxalate-extractable Al and Fe, plus oxalate-extractable P by an inductively coupled argon plasma spectrometry (ICP).

To analyze Ca and Mg effects on P sorption, a similar procedure as the previous step was used where the finely ground dry sediment of 0.5 g was extracted with 30 ml 1 M HCl at a ratio of 1:60 (0.5 ml/30ml = 1:60) by shaking on an end-over-end mechanical shaker for 4 h [22] (Pant and Reddy, 2001). The suspensions were centrifuged at 10,000 rpm for 5 min and filtered through a 0.45 µm membrane filter in the dark. The filtrates were then analyzed for HCl-extractable Ca, Mg, and P by inductively coupled argon plasma spectrometry (ICP-MS).

A batch incubation was conducted to determine P absorption and desorption properties. All of the sediments were considered under aerobic conditions. Five grams of wet sediments were placed in a 50 ml centrifuge tube and shaken for 24 h in a 10 ml solution with orthophosphate-potassium phosphate monobasic (KH₂PO₄) in 0.01 M (mol/L) potassium chloride (KCl) solution with concentrations of 0, 0.1, 0.2, 0.5, 1, 2, 5, 10, 25, 50, and 100 mg/L (ppm) P, using an end-over-end mechanical shaker at 25˚C ± 2˚C. This was the absorption procedure. Thereafter, the homogenized samples were centrifuged for 20 min at 20˚C, 10,000 rpm. Then the supernatants were decanted to 25 ml vials, acidified with one drop of concentrated sulfuric acid H₂SO₄ and stored at 4˚C for P absorption analysis. The sediment residues were then weighted and filled with 10 ml 0.01 M KCl solutions for desorption procedure, shaking for 24 h, using an end-over-end mechanical shaker at 25˚C ± 2˚C. Then the samples were centrifuged at 10,000 rpm for 20 min, decanted to 25 ml vials, and acidified with concentrated H₂SO₄. The concentration of P in the supernatants from both absorption and desorption were measured at 880 nm by UV-2501PC UV-VIS Recording Spectrophotometer using an automated ascorbic method (ESS Method 310.1; USEPA, 1992) [21].

A wet sediment sample of 40 g was extracted twice with 80 ml 0.4 M NaOH, each for 4 h by shaking in an end-over-end shaker at 25˚C + 2˚C, 230 l/min. The suspensions were centrifuged at 21˚C + 2˚C, 10,000 ×g for 30 min after each extraction. The supernatants were combined and concentrated 10 times from 100 ml to 10 ml using a Vacuum Rotatory Evaporator (R-205, BUCHI) at 25˚C. Then 0.45 ml concentrated extracts were put in a 0.5 mm diameter Wilmad NMR tube, one drop of D₂O was added to lock the signal, and then the solution was scanned at 121.4944448360 MHz on a BRUKER 300 UltraShield 31P NMR for 15 h, and the spectra were processed using TOPSIN 2.0 software. The solution composition was determined with an external standard of 85% phosphoric acid, and the NMR spectra peaks were identified by comparing the sample peaks with the differences from the reference peaks: 0.6 ml samples were spiked with 0.02 ml 10,000 mg·l⁻¹ sodium pyrophosphate (Na₄HP₂O₇·10H₂O) as an internal standard [23] (Gadian et al., 1979; [24] Pant et al., 1999).

Wet sediments (2 g) were incubated under a nonflooding condition at 37˚C for 7, 15, 30, and 45 days (d), and extracted with NaHCO₃, NaOH, and HCl sequentially as mentioned previously. The changes in NaHCO₃-P, NaOH-P, HCl-P, residue-P in the sediments during incubations at 37˚C for 7, 15, 30, 45 d from without incubation were to determine the extent of P mineralization at physiological/optimum temperature.

All the P mineralization experiments were carried out in triplicate and analyzed with SAS JMP Version 13.0 [25] (SAS Institute Inc., 2008) using two-way analysis of variance (ANOVA). A Tukey’s HSD (honestly significant difference) test was used for statistical differences at p < 0.05 level as described by [26] Tao et al. (2008). Similarly, correlation coefficients were tested on sorption parameters using Pearson’s correlation (r) significant test at the p < 0.05 or p < 0.01 level using SPSS Version.15.0 [27] (SPSS Inc., 2006). All regression analyses were performed using the SPSS 15.0 software.

No significant difference in pH was found among the six freshwater wetland sites in the Pelham Bay (Table 2). EC ranges from 87.9 at site 2 to 540 µs/cm at site 6 Split Rock Golf Course. Total organic carbon (TOC) ranges from 3.4 to 9.2. Ash-TP ranges from 337.6 to 666.1 mg/Kg (Table 2). The highest TOC%, Ox-P, Ox-Al, HCl-Ca, HCl-P and ash-TP, and the second highest Ox-Fe, HCl-Mg appeared at Site 4 beside Turtle Creek close to the Bartao-Pell Mansion Museum. The four sites close to Bartao-Pell Mansion Museum (sites 1, 2, 3 and

OM: total organic carbon, %. ash-P: the total phosphorus in bed sediments from Anderson ignition method, mg·kg⁻¹. EC: electrical conductivity, µs·cm⁻¹.

4) have relatively high Ox-Fe, Ox-Al (other than site 2, with a value of that was lower than site 6, Ox-P, Fe:Al, TOC, HCl-Ca, and total ash-P, which might be related to the sticky silty and clay type of texture, and OM could be attached to ferric (Fe³⁺) in aerobic conditions.

S_max ranges from 70.4 to 1666.7 mg/Kg (Table 3), with the highest value at sites 1-3. EPC₀ (ranging from 0.086 to 0.235), were also high indicating a substantial amount of P that remained in the sediments could be bioavailable to the water column under seasonal conditions (Table 3). Pearson’s correlation results show that Smax (P sorption maximum) is strongly correlated to Ox-Fe (after removing outlier Smax at site 4) (r = 0.89, significant probability level p < 0.05) (Table 4). The maximum Smax at site 2 was 1666.7 mg/Kg (Figure 2 and Table 3), and the Ox-Fe at site 2 was 19,166 mg/Kg (Table 2), both were highest among the six sites. The strong correlation between Smax and Ox-Fe (r = 0.894) indicates that the sediments that had high Fe content tended to have high maximum sorption capacity (Table 4). Site 1 and site 2 were mostly controlled by fine clay and silt; the soil texture was sticky for both sites. Redox has an impact on sorption. A high content of amorphous and poorly crystalline Fe under aerobic conditions results in high Smax values [22] (Pant and Reddy, 2001; [28] Wang and Pant, 2010a). The wetland area was exposed to air and ferric iron as Fe II converted to ferrous Fe as FeIII. The FeIII in both sties bound P tightly and had a high capacity to bind P [28] (Wang and Pant 2010a). EPC₀ at site 2 was 0.086 mg/L, which was the lowest among the six sites (Figure 3 and Table 3), indicating that EPC₀

K_d: distribution coefficient, L·kg⁻¹. S₀: P originally sorbed on the solid phase, mg·kg⁻¹. EPC₀: equilibrium P concentration, mg·L⁻¹. S_max: P sorption maximum, mg·kg⁻¹. k: a constant related to the bonding strength, L·mg⁻¹. K_f: P absorption energy, L·kg⁻¹.

*Correlation is significant at the 0.05 level (2-tailed), p < 0.05. **Correlation is significant at the 0.01 level, p ≤ 0.01.

was not impacted by Ox-Fe [28] (Wang and Pant, 2010a). The higher EPC₀ is mostly associated with anaerobic conditions, and ferrous FeIII is reduced to ferric Fe II [22] (Pant and Reddy, 2001). Sediment would absorb P if the P concentration in the water column was more than EPC₀ in the wetland sediment; sediment would desorb P if the P concentration in the water column was less than sediment’s EPC₀ ( [29] Kunishi et al., 1972; [30] Wang et al., 2009; [28] Wang and Pant, 2010a). S0 (P originally sorbed on the solid phase) is strongly correlated to Kd (adsorption energy), and the Pearson correlation coefficient r was 0.936 (Table 5). Pr% at the six sites ranges from 96% to 100% (Table 3), indicating that most adsorbed P was retained at a higher level than desorbed P [28] (Wang and Pant, 2010a). EPC₀ is not significantly correlated to Pr% ( Pr % =

Pr Pad × 100 % ), however, site 2 has the lowest EPC₀ but the highest Pr% and

*Correlation is significant at the 0.05 level (2-tailed), p < 0.05. **Correlation is significant at the 0.01 level, p ≤ 0.01.

S_max. The high retention ratio in the sediment made it saturated with P, therefore the equilibrium P concentration decreased when S_max and Pr% increased. Changes of water chemistry in sediments, such as pH and redox, could potentially cause massive P release to the water column ( [30] Wang and Pant, 2009; [28] 2010; [31] 2010; [32] 2011; [33] 2011; [34] 2012).

The significant correlations at the 0.01 level (2-tailed) between TOC (total organic carbon) and HCl-Ca, HCl-Ca vs ash-TP and TOC vs ash-TP (Table 4) indicate that Ca and OM bounded P could become a potential source of P in the water column under different redox conditions [8] (Diaz et al., 2006). HCl-Pi (HCl extracted IP) could range from 46% - 64% of TP in water conservation area canals in the Everglades [8] (Diaz et al., 2006). HCl extracted SRP (comparatively equal to HCl-Pi) ranged from 12% to 60%, and concentrations ranged from 73.9 to 255.9 mg/Kg in Pelham Bay wetland sediments. HCl-Pi, Ca, and Mg bound P is relatively stable and unavailable for biological assimilation [35] (Sonzogni et al., 1982). Organic P extracted by NaOH can be hydrolyzed to bioavailable P, which is associated with humic and fulvic acid ( [36] Bowman and Cole, 1978; [37] Ivanoff et al., 1998).

Organic P compounds were found in the 6 sampling sites, which could be related to the OM attached to Fe³⁺ [30] (Wang and Pant, 2009). The dominant P compounds G6P and DHAP are organic P compounds in sites 1, 2, 3, and 4, and those four sites also have the highest Ox-Fe, Ox-Al, Ox-P, TOC, HCl-Ca, HCl-P and ashP, indicating organic P is dominant in those fine sediments [30] (Wang and Pant, 2009). G6P (glucose-6-phosphate, major peak at 5.34 ppm, 81.5%), NMP (nucleoside monophosphates, peak at 4.42 ppm, 7.2%), IMP (inosine monophosphate, peak at −1.11, trace amount of 3.8%) and trace amount of PyroP (pyrophosphate) were found in site 1 (Figure 4 & Figure 5). The percentage proportion was determined by the peak area %. The major peak at site 1 was G6P (Table 6), and it had the highest TOC among the six sites. G6P appeared in all sites. DHAP (dihydroxyacetone phosphate) was the dominant compound (peak at 5.59 ppm, nearly 100%), and trace amounts of PEP (phosphoenopyruvates, peak at 0.11, 0.1%) and IMP (peak at −0.23, 0.1%) at site 2 (Figure 6 & Figure 7) were also present. There is around 100% DHAP (99.97%) at site 3 (peak at 5.16 ppm), plus trace amounts of orthophosphate (peak at 8.01 ppm, 0.01%)), GPEA (glycerophosphoethanolamine, peak at 0.47 ppm, 0.01%) and PEP (phosphoenolpyruvates, peak at −0.10 ppm, 0.01%) (Figure 8 & Figure 9). Major P compound at site 4 was G6P (4.47 ppm, 97.40%) (Figure 10 & Figure 11), trace peaks are NMP (3.57 and 3.23 ppm, 2.4%), IMP (−1.86 ppm, 0.1%), and PyroP (−5.99 ppm, 0.1%). G6P is about 100% at site 5 (Figure 12 & Figure 13). The spectra at site 6 showed an interesting pattern, with diverse P compounds (Figure 14 & Figure 15): trace amount DHAP (peak at 6.49 ppm, 0.1%), PolyN (peak at 3.65 ppm, 0.1%), and major P compounds are GlyP (peak at 5.19 ppm, 26.3%), NMP (peak at 4.25 ppm, 26.3%) and PyroP (peak at −5.14, 25.6% and peak at −6.07, 21.5%).

Compared to the Bronx River, P compounds in the Pelham Bay freshwater wetlands are quite different. The P compounds in the river bed sediments are mostly GlyP, NMP and PolyN, few DHAP and IMP. Major OP compounds in wetlands are G6P, DHAP, and small amounts of PEP [30] (Wang and Pant,

G6P: glucose-6-phosphate; NMP: nucleoside monophosphates; IMP: inosine monophosphate; Pyrop: pyrophosphate; DHAP: dihydroxyacetone phosphate; PEP: phosphoenopyruvate; GPEA: glycerophosphoethanolamine; GlyP: glycerophophate.

2009), IMP, besides GlyP, PolyN and NMP. Here, G6P might not exist in the water system because it was soluble, and it only could exist in wetland or soil environment. There are many other organic P compounds in wetlands rather than in the river. The P bioavaiability prediction in wetlands is quite meaningful; because under certain conditions, such as favorable pH, temperature, redox, the organic P (OP) could be mineralized to inorganic P (IP) and become bioavailable to plants [34] (Wang and Pant, 2012) and potentially cause eutrophication. The active P pool in the wetland sediments could maintain substantial bioavailability of P for seasonal algal growth under changing hydro-climatic conditions.

The phosphorus pool changed during the mineralization for 7, 15, 30, and 45 days under flooding incubation. NaHCO₃ increased from 43 to 57 mg/Kg during the 7, 15, 30, and 45 day flooding incubation (Table 7, Table 8). The high content of NaOH-P in sites 1 - 4 is associated with the high organic matter in those sites, correspondingly dominant OP compounds, and those sticky, silt, and clay, and sandy sediments that are associated with Fe, Al, and under changing redox conditions, could have resulted in high Smax or high EPC₀ ( [30] Wang and Pant, 2009; [32] 2011).